Step 1: read the handbook. Battlemind is a delightful class, but complicated.
Step 2: Read the art of defending. and MMO mentality. Defenders who try to get everyone in the battle to focus on them... die. The battlemind will be protecting the squishy warlock, and should aim to take 2-3 monsters on at a time.
A wis secondary will get you battle resilience and Iron Fist. Grab Vicious Cobra Strike as your second at-will, and make sure to have a heavy shield and scale armor. Living fortress does what it says on the tin, as cover makes you even more annoying to hit. Oaken Resilience at level 2 gives you another resist, and Shade Strike at 3 gives you concealment. Aim towards getting Radiant Recovery through Deva Heritage if you want more THP as well.
With THP from RR, and concealment from shade form, it's quite possible to go through a battle without taking damage. At level 1, you will take damage, but the leader should have you right as rain in no-time. Make sure you're getting the THP from the leader until you can generate your own.