Rule number 1 : Don't throw away gray items, sell them.
Rule number 2 : Buy BIG bags to stock items before selling.
Rule number 3 : Don't buy stuff on the AH for yourself, get quest rewards.
Rule number 4 : Get 2 gathering professions and sell on the AH
When my rogue hit 60 he had 400 gold in the bank AFTER having bought his epic mount.