1 .- Always keep the GPS off and turn it on only when necessary.
2 .- If you are not connected to a WI-FI or Wireless Router off this feature.
3 .- Keep the screen brightness down as much as possible but visible, do not use high gloss as it kills the battery very quickly.
4 .- Setting up synchronization of emails every hour it's a very good deal if you do not work for company or do not need the emails for productivity. I would suggest to set it up sync it manually and sync whenever you want to check the mail. This will save 15% to 25% of battery.
5 .- Use a wallpaper in black color as the display consumes less energy to produce dark colors.
6 .- If the version of your OS is Froyo (2.2) and you use a Task Manager, uninstall it, Froyo has the ability to manage applications without making your phone slow unless you have too many apps that needs to have internet access and you have them all on like Pandora, Facebook, IM and playing Angry birds.
7 .- Finally, do not use vibrator state (unless you need it emergency) as the smartphone uses a large amount of energy to produce the vibration.
This will kill your battery!!!