You sound like you're playing solo. You didn't mention your team.
This is probably gonna sound obvious, but as a mage you need to focus the bruisers, and vice versa, your bruisers focus the casters. While it's true that there is no physical resistance, it is still the mages that deal insane AOE damage and cc's. Not the physical fighters.
You also want to maximize the effectiveness of your damaging spells. For example, casting Rain first to cause Wet and reduce their Air/Water resistance. I don't know what schools you're focusing on, but it's best not to spread your points too much early.
Or, let's say you have Supernova. That spell deals huge damage, but hard to use. It centers on yourself, has small AOE, and also damages yourself. So if you want to make full use of it, you probably want some teleport-type spell like Phoenix Dive or Cloak and Dagger, to easily get yourself into good position. Also some way to buff your magic armor cause the spell damages you too.
That's the idea. I mean, I have to say that, to really maximize your combat power, you want to combine spells from different school so that they "combo". Personally, I had Lohse going with Air/Water, and I think that combo is crazy strong in terms of both damage and cc potential.
