I know, I know. We have a MILLION gold guides. But this one is neat. Most of it is the common stuff, but I like it anyways
Gathering Professions
Once you hit level 5 be sure to pick up professions there so you don't outlevel your professions and have to go back and work extra to catch up in them. My suggestion is to pick herbalism and mining. Skinning is also a decent option but you won't make as much money as with the other 2 until higher levels. There's really no point of switching over to another profession until 40. (I'd only ever drop one profession though)
Look Out for Deals
NOTE: Make sure you get Auctioneer (and update it a few times a week)
Whenever you're buying something from another player start with a low (not too low) price. Unless you REALLY need it don't budge too far from that price or they'll work you over the norm. Same with selling, start with a higher price.
When people are selling things you can just click on the item and auctioneer will tell you how much it has been going for on AH. I only ever buy Weapons, Armor, and Trade Goods. Trade Goods is probably the best type of items to buy to resell for more money. Use your common sense. Always list a little under the rest of the competition.
Providing Services
Being a mage or a warlock is always good, you can just hang around a major city and provide people with items (healthstones, food, water) or summon/port them places. This is especially good for alliance because many NE's want to be summoned over to Eastern Kingdoms. As a warlock, you can always sell soulstones every 30 minutes for a decent amount of money.
Attunement
No one likes getting attunement for end-game raids. If you're a warlock or friends with a warlock you can go to the entrance of MC (the one where you can pick up the Core Fragment and wait there and have someone advertise in Trade or LFG and get about 1g or so for every summon.
Vendoring Trash
Never ever ever EVER sell anything besides your grays to the vendor. Look on AH and see what they sell for or ask friends or guildies what they're for. In fact, ask them if they want it. If you're not sure what it's good for or what it sells for stick it in the bank until you know.
Dancing for Gold (My second favorite; works great)
Make a female alt and run them to a main city. Works best with Ironforge and Orgrimmar as they're the most crowded. Go jump on top of the mailbox (in front of the bank) and dance. Make a couple macros saying dancing for money different ways. Like "Dancing for your entertainment. Tips appreciated". If you want even start opening trade windows. After you're done with this send all the money you made to your main then delete and make another as some people like to ignore beggers.
Being a Bum (My favorite! Dont do it on your main, figure something else out! Dont make a fool of your Guild!)
Might not be the best way to get money but definitely a fun one. For a better effect make a new char and send their clothes over. Unequip all your gear and just put on that stuff. Sit somewhere where lots of people pass. Like at SW Gate.
Having a pet will help. Make macros like /em tells %t that you're very hungry. And after that line in the macro do something like /say Please, I need money to buy food for the winter. So say that you clicked on your mechanical squirrel it'd say "Your_Name tells Mechanical Squirrel that you're very hungry. Please, I need money to buy food for the winter." And you could make another one that said /em whispers something to %t. /say Spare change?
Begging for "Flight Money" or Armor Repairs.
Asking for money for armor repairs only works if you're at a higher level really. But if you stick around a flight path people will run by on the way to the flight master and you can tell them you need money for a long flight. You'll get the money then they'll fly off. This will work better if you talk in tells so other people don't know.
-Many thanks to rabidsoccerball, a member of a different forum.-