Try every available class at least up through level 15. That means rolling one each of a priest, paladin, hunter, warlock, warrior, druid, rogue, shaman, mage and playing them all. Give them each a gathering skill and a crafting skill. Get at least one of each type of skill amongst all your toons. Share materials and drops between them. You can only share materials and drops if they are all on the same server and of the same faction.
By level 15 you'll understand each class's basic game play style. Decide which you like best and play those. Make bankers out of the rest. It'll also help greatly on instance runs since you'll have a better understanding of what to expect from your team mates and what you yourself should be doing.
Edited, Apr 28th 2008 12:43pm by ItsaGaAs