Every so often, I get asked something to the effect of "What's the fastest way to get 10,000 gold?" It's usually asked by someone who is perpetually poor in game and is looking to get a BoE or some other sort of reward that costs gold. The fastest way for me to get 10,000 gold is to log in and check my mail. My daily haul is many times that and scales based on how much time I have to craft, list, and relist. This isn't a useful answer to someone who lives paycheck to paycheck, though. So what advice would be helpful?
First off, if you're below level 85, get to level 85. This nets you quite a bit of gold simply from quest rewards and vendoring gear you acquire. If you're already level 85, the first thing you need to do is identify how much money you can make per hour running 5-mans for valor points that you can use to sell BoEs. On my realm, I could sell a BoE costing 1,650 VPs for about 10,000 gold. That means every valor point I earn could be worth 6 gold, which makes the 150 points I get from a 5-man worth 900g. I can do seven per week per character with the requisite gear. Also, every trash kill and boss kill has a chance of awarding you with valuables, including enchanting mats (if someone can DE) and BoEs.