Reduce the screen brightness and set a shorter screen timeout.
Turn off radio communications (such as Wi-Fi, Bluetooth, GPS, etc.) that you're not actively using. (Note that the GPS receiver is only turned on when you’re using an app that makes use of it.)
Turn off automatic syncing for Gmail, Calendar, Contacts, and other apps if you don’t need it.
Use the Battery saver feature (accessed in the Settings menu) to control data activity, Wi-Fi connection, Bluetooth connection, and power used for the device such as screen brightness and notification light.
Allowing other devices to use your device's hotspot connection will drain your battery more quickly.
If you accidently press the Power/Lock Key while the phone is in your pocket, the proximity sensor prevents the screen from turning on in order to save battery power.