My android is draining alot of battery....?

-I have an Xperia X10. Everytime before i sleep, i charge me phone fully and use a task killer to kill all the running apps, the next day my battery life dropped from 100% to 69%! Is there any android app to extend thw battery life? Or any useful tips?less the screen brightness

menu > settings > display > brightness > less the brightness
possibly you dont lock your phone, to many txts or calls orrr a live background with many features