How to keep your iphone battery up?

I've had an iPhone 4S since September and the battery is terrible by now. It's gone down 15 percent in the last 25 minutes. What do you do to keep your battery up? Please don't say "don't use it"?

Keep charging it

Iphone battery tips: http://www.gatorspit.com/tips/iphone-battery-save.html

Don't play music too much on it, dim the brightness, the more dimmer the more battery you preserve, try not to have many programs open at once. I have the new iPhone 5 and the battery life is great however I'm always on Instagram and kik messenger and always texting so it comes from 100-23% in no time. Keep only important programs open and it should help. Also let it charge each time to 100%