We (me and the cats who provide moral support from the couch) do not condone the following: buying gold, botting, hacking, or using the /spit emote. All of the aforementioned activities are just so...disgusting.
This is some of the easiest advice I could ever give you - want to make more gold? Die less.
Now, before I get hateful comments from people let me specify: death during guild raiding - especially progression - cannot be helped. You are going to take one for the team, and you’re going to take it good and deep in the pocket. That’s part of being a team player. I always try to have a healthy cushion of money with me on raid days, and so should you. This gold is not near and dear - it’s the gold that pays for sunshiney faces and the ecstacy of making a home run on Yogg-Saron’s tummy (he has a mouth so he simply must have a tummy...somewhere).
What I’m talking about is being cautious. When you’re out there questing, solo or otherwise, you make many decisions that may or may not result in your character’s death. A death means paying for damaged armor, and if you do that a lot, you’re not spending your time productively or well. So how are you cautious?
If the quest recommends two players, why not bring three? Or four, for that matter. Suddenly the likelihood of everyone dying to the random elite mob has been reduced. Of course, if you can bring someone who is amazingly uberawesome with you, then two may be fine - but look, you’re thinking cautiously! By picking the best people for the job, you’re reducing the likelihood of death, and therefore a repair bill.
When you solo, examine the area your character is playing in. How quickly are the mobs respawning after you kill them? How many are there? How close together? By pulling a mob instead of blindly running in, you often reduce the chance of visiting the mortician/Spirit Healer yet again.
Don’t beat yourself up when you die - deaths happen, as frustrating as they may be. If you play a class like a rogue or a hunter, you can resort to using spells like Vanish or Feign Death - but many classes have ways of skedaddling and avoiding the dirtnap. Warlocks can use their voidwalkers to bubble while they run, while paladins and priests get a bubble as a spell. Shamans can tremor totem and run. Mages can ice block, death knights can eat their ghouls, and warriors...well, they live for a while, kind of retreat, and then make a nice puddle of flesh on the ground.