You can increase your speed or take the Glass Cannon talent at 5. You can use haste type spells (wildfire from pyro for example).
Also a few more tips:
- always focus on killing one enemy. AoE spells are great in total damage output, but three almost dead enemies harm you more than two at full health.
-use summons to soak hits. enemies like to target them.
-use terrain hazards to your advantage. enemies don't like crossing them so you can use that to make your ranged characters harder to get to
