ummm..
there are a few things you can do:
1) Make sure you turn your brightness down pretty low
2) dont keep the battery near a heated item because heat kills batteries quite quickly
3) try not to turn it on and off too many times and dont sync it that often with the computer
4) Lastly, DONT use your internet A LOT because it makes you phone contact wireless servers and with those servers it uses A LOT of batter
Hope this helped Good Luckk