1. Lower the screen brightness
Reduce the brightness by 50% can save you a lot talk time than you could have imagine. Best of all, most of the time you wouldn't notice the on screen difference at all.
2. Lower backlight duration
After all, you don't usually need the backlight to stay more than 10 seconds on idle. Starting with the lowest possible and then move it up if you need to.
3. Disable unnecessary sounds
Turn off unnecessary keypad, gaming sound.
4. Turn off Bluetooth
Remember to turn the bluetooth or Wi-Fi off when you are not using it. Bluetooth consumes energy even if no data is transferred with another device.
5. Turn off your 3G network
Only turn it on when necessary is a good practice.
6. Skip the games, mp3 songs, web browsing and photos
You already know this. You have no choice but to refrain from gaming when the battery is running out, even if they are addictive.
7. Listen to mp3 at the lowest volume possible
It is best to avoid playing any mp3 if your battery is low, but if you absolutely need some songs, turning down the volume could help to preserve some battery.