Here's my 'tips for noobs' thread on my guilds forum. Note, it's long but it will greatly help you get through those 'new mmog' pains. :)
Things a noob should know.
The fastest way to get to any city is to click the PvP button on the top left of the screen, and click 'Be In The Mists'. Once there you'll find an Asura Gate (a big round buzzing portal thing) that will take you to Lion's Arch, the 'central city' of the game. Not to far from where you enter the city you'll find a platform with 5 Asura Gates in a ring, these each lead to the cities of each race. It's a heck of a lot cheaper doing this than just using a WP to your home city (especially once you get a few zones past the starter one). WP cost increases based upon your level as well FYI and cost increases with level so learning the best routes to different areas of the world will save you a lot of coin at later levels.
Buy gathering tools as early as you can. They cost ~1 silver in total but allow you to gather all the basic crafting materials like wood, plants and ore. You get solid XP from gathering and can either craft with those mats or sell them. Ore in particular sells quite well, as does cloth (which is a drop, not a gather).
By the same token as above, buy a Salvage Kit. You'll get a lot of drops that say 'salvage' item on them, you can get a salvage kit and use it on them to turn them into crafting mats, sometimes Fine or Masterwork (blue and green) mats. You can salvage just about any gear items that drop too and I recommend salvaging white gear but not blue, unless it will produce cloth. Anything blue or green you cant use - or don't think you'll use them on an alt - I recommend selling to a merchant or, if you can get over-merchant price (see below), on the market. At level 1-20, just use the cheapest salvage kit. After 20 get a Basic one and you can use that all the way to 60 or so before you'll want better ones. By 80 you'll want to craft a mystic salvage kit.
Every crafting material has its own bank space, so don't fill your (limited) bank with mats accidentally. From your inventory you can deposit all crafting mats strait to your bank without having to find a bank NPC. Click the gear in the upper right corner of your inventory and select 'deposit all collectables'. It is that easy. The crafting system is quite unique as well as unlike many MMOGs, crafted gear is actually useful to you at all levels, where as in say WoW, most stuff you craft isn't remotely up to par with what you find in dungeons or world drops, accept at level cap.
The AH in this game is called the Trading Post because it isn't an auction system. You can access, buy and sell items on it from anywhere, though you need to find a TP NPC to receive purchased items or money you make. Open it with O (it's a few tabs down on the left). The main page shows the top items on the market, most traded, most desired, etc. You can sell your mats or any gear you find on here if you like, or find new gear rather cheap. You can even make 'buy orders'. If something you want is selling to high for your money, you can put in an order at a lower amount and some folks who want to sell their stuff might accept your price. Vice verse, if your selling you can instantly sell to buy orders for less or set a higher price that might take longer to sell (but if often worth it). Just an FYI.. an unfortunate side effect of this amazing market system, a lot of folks have used it as a trash bin, just selling at the lowest price they can get. For this reason a lot of items (gear most often) sell at prices BELOW what you can get from a regular merchant because of the selling fee. So if you pick up a green (masterwork) weapon that sells for 51c to a merchant and 54c on the Trading Post, do note it will show the money you'll make 'after' the fee is taken out and more often than not it'll be lower than the merchant price. So only sell gear on the market if you will receive more than what merchant will give you. Unless things change you'll find most the time blues and greens are better sold to a merchant NPC, especially at lower levels.
One thing a lot of folks find confusing about items in the game is the GW2 item color code is different from most other MMOGs. Most MMOGs follow the WoW formula of white - green - blue - purple - orange. This might be the standard but it doesn't really make any sense. It is as if it was just chosen at random. GW2 uses the more logical colors of the rainbow, only in reverse. White - Blue - green - Yellow - Orange - Magenta - Purple. (R.G. BIV in reverse). Do note that greens are 'better' than blues in this game. At the top of the spectrum is Orange, exotic level items (lvl 70-80) and red for Legendary Weapons which are the hardest weapons to get in the game. They did just recently add a new color, Magenta which is only used for Ascended gear, items used for the latest dungeon's hardest difficulty levels (yes, the game has a dungeon that becomes harder the more you do it and each time you do, you do 3 of the possible 9 'wings'.)
You may have already noticed (if you've gotten a character past 15 or so), but the game's levels are quite lateral in design instead of linear. You can gain your levels XP and even drops no matter what level the area you are in. You get down-leveled automatically as you play if you are in areas lower level than yourself. You'll notice (even at lower lvls) a little downward green arrow with a number in green beside it. This is your adjusted level. You don't lose any skills or traits, your stats are just automatically reduced. But the benefit of this is that you can level your character however you want. If you 'really' love a particular zone, you can stay there as long as you like and still advance. The amount of xp you gain outside of areas your level is about 80%, and you have a chance to get drops that are within ~5 levels of yours. For those at 80 they can actually get 76-80 exotic drops in almost any zone.
Every time you do a zone, make sure you work toward getting 100% completion. Each time you zone into a new one it will tell you how close you are and if you bring up the map it will show this in the top left. You get completion by doing every heart, getting every skill points, finding every point of interest and vista. Once complete you get a nice boost in xp and some handy gear.
When leveling some people find they complete a zone but are still not high enough level to do the next. For example Queensdale the Human starting zone is 1-17 zone and some people complete it by lvl 14 and have a hard time moving on. In this case a lot of folks will do content in other races starting zones. In higher levels there are at least 2 zones for each level range to level in. I personally have never encountered that issue for one reason. Everything in this game gives you xp. So I recommend in participating in everything you can. When you do an event, wait around for 1-2 minutes because often the next event in a chain will start. Harvest everything you find because it's good xp. Crafting is great xp, you can pick up a level or two in an hour easy. Also do your personal story at each level that you can. They are good xp and reward level-equivolent gear and useful items. If you do each, you'll probably never be under-leveled when you complete a zone. The reverse is true for me, I very often quickly advance past the zones 'level range' far before I complete it. But with GW2's downleveling it doesn't really matter.
Advanced Tips by Swett
Combat: Timed movements and dodging are key to survival. Remaining still is death. In larger dynamic encounters, spastic movement will get you killed. While certain classes can provide healing support with aoe heals/regens, everyone is responsible for their own well-being (e.g. seeing and standing in an aoe regen area, dodging at right time, using self-heals, etc.).
Crafting: Crafting is great xp, but some folks start crafting and find it levels dramatically slow. The key to this is to experiment. On the top tab of the crafting UI the menu will show every ingredient or material you can and you can combine various ones to create items. Many times this follows a pattern, craft two parts 'sword base and blade' and combine with Inscription/Insignia/etc and create an item. It's great xp and you can level both crafting and your character really quite fast by crafting. While on the crafting menu you can access your bank and the discovery section actually will include all mats you have, both on your character and in your bank. At lower levels many zones will have a 'crafting village' you can use for quick bank access.
Crafting Materials: Fine (blue) materials are rarish drops and are the real pinch point. Each flavor of an item requires a certain fine mat, like vials of blood for strong and claws for precision. You can only make parts with common mats like cloth or ore. It takes 3 fine mats to make one fine (blue) item and 8 to make a masterwork (green) item. Rare (yellow), or higher quality items use even more. Most mats are used by at least two crafts except gems and ingredients are mainly used by Jewelers and Chefs. Some intermediate items/parts do not have pre-set bank slots and take up normal inventory space, most predominantly 'crafted' ingredients in cooking and 'parts' like armor padding that you make and then use to make the item.
When crafting you get the most experience from Crafts Jeweler has the fewest recipes (3 base items) to discover and exp off of. Chefs quickly consume inventory space with the number of ingredients they make. Huntsman (7 base items) and Weaponsmith (8 ) require more fine mats to discover all recipies. Artificer has fewer base items (4) but also makes potions and sigils which require rarer items. Tailor, Leatherworker, and Armorsmith make 6 base items and bags/boxes.
Craft Selection: You can learn every crafting discipline without losing any recipes -- you simply pay some coin at a trainer to activate a discipline in place of another. Your inactive crafts are just that, inactive. You don't lose crafting levels or recipes. Most folks go with Jeweler + Tailor/Leather/Armor as their first pair of active crafts to cover most slots. Recipes to make rare (yellow) and exotic (orange) items are available from Master craftsperson vendors for karma. They also sell required items like jugs of water, thread, coal for smelting. Runes of holding are required for bags and cost between 10s and 10g from the vendor depending on the tier.
In addition to the recipes discovered during crafting, many recipes are only available from vendors and usually for karma. There are also area renown heart (quests) you can do to unlock karma merchants -- these are the yellow hearts on the map. A filled heart means you've unlocked that karma vendor. Most will only sell items but some will sell special recipes. Similarly, at the end of some events an npc will turn into a merchant. Notably, the end-game temple merchants offer exotic armor for 42,000 karma/piece. These are only accessible immediately after the successful completion of event and only for a short time. While all temple armor sets I've seen so far have the same skin, they each have different stats and sigil.
Events & Hearts: A great deal of new GW2 players will get tripped up when it comes to events and hearts. Hearts are generally similar to standard MMOG 'quests'. They differ in several ways. First, you never need to talk to an NPC, Hearts get automatically added to your UI as you get within range of them. They offer a variety of ways to complete them that involve doing themed activities that slowly fill a 'bar' on your UI. When finished you can talk to the NPC to purchase various rewards for Karma. Karma is gained through Events. At lower levels Events are generally found near Hearts, just to get folks into doing them. These are spontanious and often (at lower levels) cyclical. You'll notice on your map and minimap orange circles, these are Event areas. NPC's may run up to you or shout for aid and talking to them will reveal a nearby event. Completing an event is good xp and rewards Karma based on your participation (bronze, silver or gold, and it's easy to get the gold). To many people do an event and rush off to the next Heart, like jumping between quest givers, but you actually miss a tun of fun content by doing this. Rather, after you do an event you should wait in the area for ~1 minute. You'll see NPCs talking to each other, hinting at what comes next. If you wait you'll often be surprised by deep and fun events that take place over several stages that lead to a large finaly. The largest of these is called a Meta-Event that is multi-stage and moves back and forth as the players play them. For example in Queensdale one of the meta-events is in the swamp, and it leads to a huge fight with a shadowy monster. I won't spoil it, but if it pops up you'll see messages in the zone 'Behemoth pre-event starting' or 'Behemoth up!' often with a waypoint you can click to see and use.
Dailies: Try to complete the daily achievement if you have time, they reward some coin and a jug of 4,500 karma. (with karma boost can be 6,250). Unlike most MMOGs were 'dailies' are static quests you do the same 10 or 20 every day. Dailies in GW2 are achievements. Open your Hero menu (H) and go down to Achievements and you'll see the first category is 'Daily'. You'll be able to select 5 of the variety of achievements that change each day. Completing them is easy and fun and as said above, rewards a tun of karma. Early on it doesn't matter how often you do them and you can 'drink' the jug right away. At higher levels as rewards get more expensive folks generally will save these jugs and then use a Karma Booster (item you can get on the store or via Black Lion Chests, which you get keys either as very rare drops, the occasional story reward, or off the store) and use a guild Karma banner to boost their karma intake and then drink a bunch of jugs at once.
Above all, enjoy the game! This game has much to offer if you explore and listen to npcs. I think the game has incredible depth and scope. Talk to every NPC with a name, explore each zone (you'll never find everything a zone offers in a single play-through. I did Queensdale 4 times before fully finding 'everything') When you get some levels participate in WvWvW, huge server vs server vs server 2-week long battles with castles and siege engines. Recommend you find a guild that enjoys it as just joining the big zerg isn't as fun. Also you can do 'arena' style PvP at any level, it auto-boosts you to level 80 while you are in 'the Mysts'. The PvE dynamic world events and other encounters are well done and you don't have to wait for a raid to form or key class (none of these in GW2) to show up to take part. Lastly the story quest is different depending on your choice of race, profession, personal history (filled in during char creation), and selections made during the quest line. This provides a large number of unique stories to experience. Don't rush through the content, take your time. You'll level faster than you think anyway. If there was ever an MMOG where the journey was more important than the destination, this is it. :)