Reducing speaker and screen usage will help. Turn the sound and brightness on the device down. Tap the home button, swipe up from the bottom of the screen, and slide the dial to the left for brightness. Slide the dial to the right to turn the volume down.
Pressing (but not holding) the power button on the device to lock the screen is guaranteed to help out the most. Press the button to lock the screen whenever the device is not in use!