Did a little quick research and found loads of info [the title above is a good search term] but here's a synopsis:
Saving Battery Life on the iPhone - notes from articles [2/2/12]
- Go to Settings and adjust what you can to limit the constant operation of the iPhone [fetch, don’t push, mail; turn off Location Services not needed, etc.]. In iOS5 & the 4S, there are other Location settings you can adjust. turn on auto-brightness or reduce screen brightness
- turn off Bluetooth, 3G or Wi-Fi, if not needed. Usually turning off Bluetooth is not a major issue but unless you’re away from 3G or free Wi-Fi, the other two may need to remain on. Turn on Airplane Mode if you want all connection off.
- avoid using battery hogs: videos, games and Siri, sometimes.
- Some of the above
- Turn off Notifications you don’t need and turn off Push Notifications especially.
- Close your Background apps - to multitask, Apps you’ve opened remain open and available [quick two-taps on Home button shows them across the bottom of the screen] - every now and then go in and turn them off by clicking the little red dash.
- There are other tests and possibilities you can find out at the Genius Bar.