Optimize Your Settings
Depending on how they are configured, a few features may decrease your iPhone battery life. For example, the frequency with which you retrieve email and the number of email accounts you auto-check can both affect battery life. The tips below apply to an iPhone running iOS 4.0 or later and may help extend your battery life.
1.Minimize use of location services
2.Turn off push notifications
3.Fetch new data less frequently
4.Turn off push mail
5.Auto-check fewer email accounts
6.Minimize use of third-party applications
7.Turn off Wi-Fi
8.Turn off Bluetooth
9.Use Airplane Mode in low- or no-coverage areas
10.Adjust brightness
11.Turn off EQ
12.Turn off 3G (GSM model only)
[source: http://www.apple.com/batteries/iphone.html]
