Fourth is to use consumables. Healing potions, mana potions, run scrolls, anti-shock scrolls, resistance scrolls, food, and any others can give you an edge in a fight or escape. You can only have so many of some up at any given time, but in rift and Abyss PvP, they can be life savers. Even a healer should consider carrying some instant health potions. And everyone wants Greater Healing Potions, which breaks a number of nasty status effects such as roots.
Fifth, assume every Templar has Inescapable Judgement. This is that blue lasso ability that pulls the target to them. Be prepared for it and be ready to get back, especially if you're a squishy or prime target.
Finally, look for safe spots around combat NPCs. Not all NPCs, even those of your faction, will pull out a weapon and go attack the enemy when they get near. The ones that do are usually high level and at least of Elite rank. The stronger and more numerous, the safer these spots are. Take advantage of them and use them to rest. But, be careful, you can get sniped in these and a group of higher levels can obliterate you and your NPC allies.
As low as level 10 you can enter the arena. Sometimes people will camp this area and gank lowbies trying to do the quests offered there. There's no penalty or reward to get here, so killing them only slows them down. But, if you can kill the ganker, do it. No ganker means no worry about not finishing your quest.
A couple of things in the arena help specifically. First, when you enter, if you don't do anything, you'll be completely invisible for about a minute. The moment you act, this goes away. Use this to wait until people are distracted. Once you have your opening, either run along the edges or fly to the quest contact and quickly talk to him. Once the conversation is done, then you don't need to worry about getting killed. Grab your weapon and bust some heads on the way out or die trying. You won't lose anything, so why not?
In level 20+ zones, except a specific one, enemies can pop in through a portal and go kill people. Naturally, since we're talking about surviving PvP and not owning PvP, we'll be assuming you're not one of those going through the portal, but dealing with the ones coming into your faction's lands. Rift PvP isn't entirely common, so for the most part you'll be free to solo quest without interruption (at least, in my experience).
First, watch for the messages "A rift connected to X has opened," where X is either Elysia or Asmodae. The one you want to watch for is the one connected to your map from time to time and look for a skull. If you see one, that's an enemy who has killed many of your faction's players. If you don't want to try hunting it down, then avoid it. Odds are the player came from a higher level rift.
Third, if you're unlike me and can access the chat channels such as Trade and LFG (no clue why I can't), access /1, which is General. People will give locations to rifts and enemies in this channel sometimes. Use it to either hunt down the foe or to avoid them. Also, keep in mind, depending where they appear they will have different capped levels. As a general rule, the farther they entered from your zone's main town, the higher level they will be.
Fourth, don't be afraid to /shout for help. Call for help and give a location on the map. You can control-click the map to put an "x" on it and then link this spot in chat. Allied players who are actively looking to get kills can run over and help you out. Or, on occasion, die trying.
In the Abyss, you have to add a new axis to the fight for fighting. Ambushes become easier with flight as players can use it to move faster. The enemy can appear anywhere at any time and roving gank squads are not uncommon. Expect lots of combat down there.
First, Wind Serums and Raging Wind Scrolls become very important. The longer and faster you can fly, the better. People will fly a lot and you get passive abilities while in the air. Flight is usually faster than running, so chases and retreats often take to the skies. However, when in the air, you get less physical defense, so you'll take more damage. This can be important when being stalked by, say, a Ranger. If you can keep moving, you might be safer retreating from a physical attacker on the ground than in the air. And then, when they land due to the flight timer, you can get away by flying.
Second, fortresses your faction controls can either be safe or deadly to you. It all depends on whether the enemies are willing to farm fortress guards for the mass amounts of Abyss Points or would instead get farmed by the guards. If you see red dots in the middle of the fortress as you approach it, then get away! This is something that I personally think needs to be addressed, as an invulnerable fortress should... well... be invulnerable.
Third, when escaping in the air, you can do one nifty trick: stop flying. Yes, cancel flight, fall for a few seconds, and then turn it on again. It can throw off your pursuers or even make them think your flight timer ran out. If they think you started falling to your death, they won't chase you.
Fourth, though I don't have much personal experience in this, the higher levels of the Abyss seem less populated. Gank squads go for easy targets, so they'll be less frequent up there. Of course, my time on the upper level is very limited at the moment, so I could be wrong.
And finally, groups and alliances help a lot. A strong group, even a small one, can hold off a huge number of players through mind games alone. Ever seen five players bottle forty by some allies because they were too scared to rush the five? I have. I was one of the five, and I knew we'd die if they zerged us (and eventually, they realized we were few in number and did). Safety indeed lies in numbers.
If you have any tricks for making it through PvP alive, feel free to share them in your comments!