*Rule One: Pick 2 gathering professions*
Take two gathering professions initially. My personal favorite is mining and skinning because you'll be killing tons of animals anyway, why not skin them? Mining/Herbalism is not ideal because they share the same minimap (unless there's some addin that fixes it). The reason that you pick two gathering professions is simple...crafting professions require higher and higher level items the further up you go, and you'll reach a point quickly where you need materials that you can't gather yourself. And since most crafting professions don't make money until you are high high level (discussed later), you will be broke as a joke...and we don't want that, do we? With mining and skinning you will find yourself with enough gold to pay for gryphons and all the latest green items you need (heck maybe even some blues!)
*Rule Two: Invest in big bags*
Once you start gathering leathers, hides, ores, stones, gems, etc...you will quickly find that you'll fill up your bags. Skip the 10 and 12slot bags and go all 14slots. Don't worry, you'll be able to afford them faster than you think! More bagspace equals less trips running back to the Auction House. Speaking of which...
*Rule Three: The Auction House is your friend*
Don't you ever ever EVER sell non vendor trash to vendors! If it's white colored text, find out what it's used for and what it sells for, and put it up on the AH! I can't tell you the number of times i've grouped with ppl and they leave Wicked Claws on the corpse! I sell those for 20-25s each and that adds up! For the items you got from your gathering professions, find out what the price is on the AH and put it on for what you think it will sell for. Don't try to get the absolute most out of it...you don't want these auctions to expire, so make the price aggressive yet still worth it for you.
*Rule Four* Level 40? DROP ONE PROFESSION!
I know what you're saying..."Gen, I'm now a lvl 300 miner and skinner thanks to your great advice, and now you want me to drop one?!?!" You betcha arse i want you to! Now is the time you choose a profession that sounds fun to you. Don't listen to what anyone says, you can make a fortune off of ANY of the professions (except maybe Alchemy heheh). Let's say you decide you like the idea of engineering. Drop that skinning and pick up engineering. By this time you've gotten high enough mining skill, plus you're lvl 40, so powerleveling your engineering should be a breeze. You might not reach lvl 300 engineering at lvl 40, but get up there enough to start making money off of your new crafting profession. But how do you do THAT Gen? Glad you asked...
*Rule 5: Own your new crafting profession!*
Ok here's the real meat and potatoes of how you make money. It's called SUPPLY and DEMAND. See that schematic for a sniper scope on the AH? Buy it! See that schematic for thorium shells, that one for the lifelike mechanical toad? BUY IT! Why you ask? Because it's those "rare" schematics that separate you from the 100 other wannabe engineers! Every engineer knows how to make a mechanical squirrel, so it floods the market and makes them worthless. But not everyone knows how to make sniper scopes, so you've narrowed down your competition and will start to make money. Now for the tip that will kickstart your moneymaking...
*Rule 6: DO THE MATH!!!*
It's as simple as this...if you can't buy the mats off of the AH, craft the item, and sell on the AH for a profit...DO NOT DO IT! This fluctuates from day to day. One day sniper scopes are huge, the next day there's 100 on there for less than the price of mats (usually ppl lvling their profession). Don't worry, find something else to buy mats, make, and sell. Once you get the hang of it, you're going to discover "wow, why am i spending all of this time farming mats when i can buy them off the AH and still make a profit?" DING DING DING!!! EXACTLY!!! NEXT RULE PLEASE!!!
*Rule 7: Drop your 2nd gathering profession!*
This is for lvl 60 ONLY! Do not do this prior to lvl 60! This is an optional step...maybe you like mining or skinning, they both have a small use in high lvl instances, but 9 times out of 10 you'll find you don't use that gathering profession much at all. So drop it and pick up another crafting profession! At this point again you're probably rich and you're high enough lvl that it should be easy to power level that sucker (took me less than a week to lvl enchanting to 300, and that's the toughest one to level). Do the same thing as with your 1st crafting profession, buy all the good high end formulas/patterns/blah you can get.
Congratulations! If you stopped now you would be incredibly wealthy...what's that you say? You wanna be SUPER incredibly wealthy? You greedy [bleep]...I KNEW i liked ya for a reason!
*Rule 8: Do what the others deem as crazy*
Blizzard has incorporated new epic formulas/patters/blah for those who are crazy enough to work for them.I won't go into details here as there are forums that go into detail, but faction is king here! Timbermaw Furbolgs, Thorium Brotherhood, Argent Dawn, etc etc. Get ready to spend a lot of time and money to get here, but it will pay itself back with dividends.