I send all my alts 2g the moment they leave teh lvl 1-6 area and reach their second town (Goldshire, Azure Watch, etc.). On my server 10 slot bags sell for 50s each. The 2g is just enough to get the toon four 10 slot bags.
Learn your servers economy is the best way to make money.
When I used to play horde (very short while) my warlock was mining, fishing, and enchanting and made well over 50g by lvl 10 and had 1k gold at level 40. My BElf paladin was jewelcrafting, mining, and fishing. The leveling was slower than I may have liked but the constant influx of gold was great.
My first mage on another server was tailoring, fishing, enchanting. Even after using linen to level both first aid and tailoring I would usually have enough to put a few stacks up on the AH and sell them at 50s buyouts, wool for 1g. I constantly found low level blue items for 5g on the AH and would repost them at 20+ gold and they would always sell within a half hour. Had 3k on that char by level 40.
My main (linked in sig) is currently sitting on 800g. Working on powerleveling my enchanting right now so I'm spending a lot on mats and this character was naked at 60 for the longest time...
It's far to easy to make money in this game..