Without knowing what's using battery in your phone it's hard to say what you should do. There are however already several threads regarding battery drain so i recommend that you first search the forum for drain and check the existing threads for possible solutions. Here are a few examples:
http://talk.sonymobile.com/message/345179
http://talk.sonymobile.com/message/379341
To see what's using most battery, go to Settings -> Battery.
