There are many ways you can save the battery life on the iPhone. The main issue with using any of them is that you may be disabling some functions that makes the iPhone so great. It is really down to personal choice on which functions you decided to disable, if any, in order to save battery life.
But at the end of the day the remaining fact is that the battery life on the iPhone is not great,when you consider the tasks a busy iPhone must complete on a day to day basis you can see how the battery does not last very long.
How to do it: Settings> Wi-FI > OFF
Implications: Simply no wifi networks will be detected. If you never have used wifi, or have no need for it, this should of course be set to OFF all the time, if like me you require it constantly for mail and applications, turning it off is not an option.
How to do it: Settings > General > Network > Enable 3G > Off
Implications: Your iPhone will only use the Edge network, which means when you are not in a wi-fi area, that video and tasks which require large amounts of data will not run at an acceptable speed. If you are mostly in a wi-fi area, or do not use much data, you might consider disabling 3G.
Disable location services
How to do it: Settings > General > Location Services > Off
Implications: You will be unable to use your GPS location or any GPS services, such as google maps or a GPS navigation application, you can disable this if you do not use any of these services, or disable GPS and use as required.
How to do it: Settings > Brightness > use brightness bar to reduce or increase
Implications: Your iPhone screen brightness should be at an acceptable level which allows you to use your phone without straining your eyes. You might find that you can reduce the brightness to a lower level that is acceptable.
Use auto lock
How to do it: Settings > General > Autolock > Set time
Auto lock is great if you forgot to power off the screen when not in use. Setting to 1 minute will save you that little bit extra battery.
Remember when you are sitting at your desk at work or in the car use your charger where possible, until Apple work to give us a stronger battery life we are left with disabling these services.
Finally, let us know any of your tips on saving battery life on the iPhone.