how can i make my battery last longer?!

Oh ok.  You probably have the free version of advanced task killer then.  I don't recommend you to get the full version because it will start mess with core apps and it can get pretty ugly.

I don't really use auto kill function because ATK freezes up my phone sometimes when multi-tasking.  I set everything manually.

However, if you want auto kill on:
1. press hard key on the very left bottom(the one next to home key) and press setting.
2. 'Check on auto start' and 'show notification'
3. Set auto kill level and kill frequency.  You can set this as aggressively as you want; ATK free version is quiet friendly.
4. leave everything alone.

Ignore list (When you first open your ATK, long press apps to ignore)
foreground apps: daily briefing, voice commands, google voice. Mail apps are synced to your phone, so you can set 'em to kill.
background apps: anything that needs to be turned on 24/7 such as fancy widget, clock apps, extended controls, etc etc.

Best ways to do it are auto task killer and turn off live wall paper. The internet kills battery life quickly as well.

Don,t over charge it!
brightness should be less!
remember to close any open app's
and when you are talking on phone try to use hands-free so that your screen will be not active!