Reduce the screen brightness setting and set a shorter screen timeout.
Turn off radio communications (such as Wi-Fi, Bluetooth, GPS, etc.) that you're not actively using.
Turn off automatic syncing for Gmail, Calendar, Contacts, and other apps.
Monitor the Battery use screen to identify if apps you've downloaded are consuming a large percentage of your battery power.
Allowing other devices to use your phone's hotspot connection will also drain your battery more quickly.