I just made it to paragon tier! My wizard Bai has been focused on area damage with some control effects, especially slowed (save ends). I use Orb Mastery to make the opponents' saves more difficult for powers like Horrid Whispers and Twist of Space.
Defensively, I've been a get out of the way type, using Wizard's Escape to not be there for the attack in the first place. That's worked well when I've been able to stay behind the party. I'll still get hit a couple times before the end of combat, but it usually doesn't become dire. I actually believe I've done well at not being a sink hole for the cleric's powers.
This all is changing because I've taken the Blood Mage paragon path.
Now that I'll be taking damage much more often during combat (from the wounds I deal to myself!), I need to figure out a way to keep myself from dropping. So it looks to me like my strategy needs an update. (If I'm wrong, tell me why.)
My idea so far is to do healing on myself which might let me keep up with my own damage. Also, I think I read about some magic item that let you gain regeneration 5 when you're bloodied. I noticed the Heal skill powers in PHB3 which would let me spend a healing surge as a minor. Beyond powers and feats, I'm looking for good strategies and new tactics that would require minimal retraining, though retraining is not off the table. I'd also welcome any ideas for useful items I could put on my shopping list.