I see a lot of people (on 2 servers) saying it's not easy to make money.  Some of them are talking about making bucketloads of money but most are just struggling to make ends meet.  At the risk of handing the gold farmers all the tools they could want, I'm going to keep it to generalised tips just to help those struggling.

First of all simple game mechanics that help:

Crouching.

Crouching will do a couple things for you.  First, if your weapon gets a beading bonus, you will do significantly more damage and therefore reduce your ammo expenditure.  The second thing crouching does is reduce the incoming damage from ranged attacks (getting shot).  This, of course, helps you live longer and also helps reduce your equipment repair bill.

Cover.

Same as crouching above for reducing damage and associated costs.

Weapon Range.

If you fire a weapon when it's range meter shows blue, you are doing reduced damage.  This, of course, costs you more money because you need more ammo to kill things.

The Right Weapon.

This follows on from above.  Using the right weapon for the job is also important in controlling your ammo usage.  Using a shotgun, for example, can be incredibly cheap on groups of 3 or more enemies if you can hit all 3 at once.  Against singular targets however, they are very expensive (3 "bullets" every time you pull the trigger).  Also, shotguns have no beading bonus and a short range.  It is definately cheaper to crouch and use a rifle as your enemies close in on you if you have the luxury of range.  Of course, the "right weapon" can be very open to debate.  It depends on your class, your pump level in a given weapon skill, it's colour and the situation.  I'll leave it up to you to make the choices.

Enemies in cover.

If you can help it, don't shoot at enemies in cover.  Back up to draw them out of cover, close in, or find another way to flush them out.  Damage to enemies crouching in cover can be as little as about 30% (conservitave number) of what you SHOULD be doing.

Weapon Skills.

You shouldn't use a weapon under Pump level 4 if you can help it.  The extra damage from the skill will save you a LOT of money on ammo.  Damage add skills, of course, will also achieve the same result.

Damage Skills

These are usually either free or very cheap to use.  Damage done with skills = less ammo bought.

Pets.

Depending on who you talk to and what class they play this is a hot topic.  Pets from all classes, if used right will save you money.  As pets are often just rediculously stupid and quite hard to get to do anything, the time taken to make them attack is just not worth it.  You could make more money shooting the things yourself.  The exception to this is the Engineer.  Engineer turrets actually do a good job because they bypass the problem of the incredibly short leash that most pets are on because turrets can't move.  This, of course, can be a drawback as you round a corner and they no longer have LoS, but "pulling" mobs back to your turrets works well. They will pick out targets and keep firing until they are sure it's hurt enough thus doing a considerable amount of damage.

Beyond that we have farming.  I'm not going in-depth on where and techniques, but offering some basics.

Kill Count.

No matter what the class you play, it is important to optimise your kill count.  For some classes, having too many enemies is bad, for others having not enough is bad.  It just depends on how you play, your weapons, how much damage you can do and whether you can heal efficiently.  Try to find a place you can kill with frequency, but not so overcrowded that your weapons overheat or you die all the time.  Some classes are, of course, better able to keep the kill count high while not dieing or ending up having to swap weapons all the time to avoid heat.

Bosses.

The special bosses you chase for ToO's and missions sometimes don't follow this so be wary.  Bosses usually offer 10x the cash reward for killing of a normal mob of their type.  Try to farm an area with one of these bosses in it.  Although harder to kill, it usually takes you only 2x to 3x the ammo to kill a boss, so you are getting 10 kills for the price of 3 where the bounty (credits for killing) is concerned.  Bosses are also more likely to spit out items better than green and large piles of ammo.

Control Points

To make this perfectly clear:  Control points are TERRIBLE places to get money.  Due to the rapid kills and effectiveness of AoE weapons they are good places for farming XP, but terrible places for money.  Here's why:

Loot at Control Points is terrible.  Schematics, ammo and item drops are FAR below the average anywhere else.  Yes, the money comes in thick and fast, but you are using ammo at a fantastic rate as well.  Even for Engineers who can cheaply pump out the damage you can simply farm money faster elsewhere simply because the item drops are far better.

My Personal Preference:

My personal preference for farming is the Engineer.  It's not that that you make more money because, if you play your cards right, turrets work out dirt cheap.  They DO, but I can make the same amount of cash (after expenses) with my Grenadier, Guardian, or Exobiologist (probably my Medic too).  It's the fact that you can go out, find a spot, set up, keep yourself occupied, and not die all the time.  It's boring running back to where you were but with the Eng you can pump out the turrets and be damaging while you heal.

I'm also just a pet class kind of person.  But money is not uber hard to come by even if you aren't an engineer.  All it takes is to be a little careful or farm once in a while when you find a good spot and you should do just fine.

Good Luck and Happy Hunting ;)

There is something I would like to add to the excellent advice above...

Going to a lower level area and killing lots of MOBs may not net you as much as you might like... The cost of higher level ammo can even put you in a negative cashflow situation!

Hunting "at level" , or slightly above, MOBs seems to produce the better cashflow for me.

I haven't tried using lower level weapons on lower level MOBs to see how that works out... Someone else will need to comment.

I haven't really had to worry much about credits. I'm halfway to level 30 and have around 1.2 million credits. Mostly every piece of gear I have is from the Military Surplus Auctions. Ammo doesn't cost that much at all for my exobio at least. I haven't heard anyone going broke or needing to farm for creds.

It's not hard at all to make credits, especially with the Military Surplus finally being added to the game. 

Started 3 days prior to launch and saved my credits that I got from loot and missions as well as all of the yellow, blue and purple loot I got.  Only spent credits on what I needed, didn't splurge on anything.  Made sure that at first, most of my weapons used the same ammo type.  Saved on costs of ammo.  Saved all the paint schematics I looted and sold all other schematics.

When the Military Surplus was introduced, I placed all my good loot for sale as well as all the paint I made from the schematics I looted.   From doing that, I've made over a million credits.

It makes me laugh knowing that people buy credits when it really is very easy to get them in game through normal means. 

Subotai Fuhyo

I've been looking through the different classes and exobiolist with full motor assist at pump 5 seems to be the cheapest class to maintain and you can kill mobs with corpse explosion (which may benefit even more with next patch from attributes) with little weapon use, while grenadier seems to be the MOST expensive which I would avoid for farming with. I have seen some even going guardian for farming but the staff dps seems to be less effective than most other classes.

money never matters in TR

Making money really hasn't been that big of an issue, grenadier is by far the most expensive to maintain that I have seen but some say it's still doable. When I'm making a farming alt I would only wear greens and maybe blues since purples costs a freaking fortune when you need to repair. Spy and exobiolist or maybe engineer seems to be the most suitable for farming with little need for ammo.

Edit - hmm I posted again in this thread, I thought it was a different thread. Oh well.

As well most MMO's Expansion get expensive when your expected to cough up some heavy coin for that new vehical or that top weapon somebody just made. Collect your coin for that point in time where ammo isn't the only thing needed to purchase, I know I am. See you at the front

Great post, and worthy of a title!

I would also like to add that I found farming with a friend to be  worth it, sure you  share the loot, but you rack up twice to three times the kills due to numbers and damage. I (a Guardian) went farming with a spy and we found ourselves to be a great team, playing to each others weaknesses.

Also I would like the add that I feel the best zone I have found (at the risk of RMT reading this) So far has been Mires. At level 30, up in the bane mineing place (outside) there are plenty of bosses and tons of regular mobs, we came out with a bag full of blue/purple items.

Cheers.

Thanks for these hints!

I've just started playing, and in the long run these tips will come in handy

I found it faster but a little bit more risky to kill mobs using shotguns and ability's than killing them 1 by 1. Its also good to go into instances with a group the shares are lower but you get more bang for youre buck using a group. =) (hope this helped)