1. Skinning and mining ASAP (this should be around lvl 5 for most characters)
Reason for mining and skinning is simple, there is a demand for leather and ore/gems from lvl 1 -70. both sell well.

2. Bags, bags, bags..
For about the first 10 or so levels you wont really need bags.. but as soon as you start sellin your first stacks on the AH.. get 4, 6+ slotters.. and slowly upgrade to 14+

3. Pick up EVERYTHING
Selling all grays to vendor. Whites and above on AH. pay a little attention to the whites that dont tell after posting twice.. and just vendor them..

4. Dont buy anything
if its on the AH. its over priced. all the gear you will need to lvl 60 and beyond you can get through questing, plain and simple. Water and Food are KINDA the exception.. i say kinda because you can skip buying food and water with some careful planning of first aid and using items you pick up..

5. Spells and Abilities
if you know your not going to use it. dont buy it.

6. Fishing
you can make alot of money on selling things you fish for, with only spending a little of your time. cooking and eating fish is also good for saving money too.. less food to buy elsewhere.