I'm not sure you do, really. Not now at least, with balance the way it is.
At the moment, at least for the weapons I've tried, fire does far more single target and AoE damage than Ice or Air. Ice does some healing, but not really enough--you'd be better off killing your targets much faster with the fire spells. Air is just far too weak--it's supposed to be the single target set, iirc, but it does worse than Fire's aoe skills there.
For example, Fire for scepter gives you 101, 756, and 571 (aoe) damage. For Air, it's 91, 403, and a blind attack (cause your opponent to miss the next attack. Dagger offhand for fire gives you a big Aoe that causes a burning effect (and gives you might when you use phoenix) and causes 403 damage, and the second skill is 941 in a cone in front of you, with a bonus to burning foes. Dagger for air gives you an AoE that does 336 to your main target, then hits nearby targets (dunno if it's the same or less), and a knockback+swiftness skill.
Really no reason whatsoever to use Air in PvE right now. Just stick with fire until everything is balanced. Water is fine if you're grouped, but don't rely on it when solo. I have no clue when Earth becomes available...
Anyways, you all are horrible, @#%^ed up people