How to make my iPhone battery last longer?

Whenever I use my iPhone even a little, and when i'm on an app for a little it loses like 2% every 4 minutes or whatever. How come? Why does it drain so fast? I kill all the apps, I turn everything off, Wi-Fi, blutooth, those are off, auto brightness is on, my screen brightness is lower than half way, what's going on?

First full charge your iphone, after that switch it off and keep plug in charger for 12 hr then switch on your iphone. It will increase your battery life i tried it myself. Moreover close apps which you are not using at the moment. Still if it don't help then you better go and ask in service center.

Turn the brightness down even more
Plus watch this video

App games
Brightness on the phone
Texting/Calling
Internet

App games are so much fun though, alot of word games =P