1. Turn Off Wireless Communications Like GPS, Bluetooth, Wireless
2. Adjust the Brightness : Go to Brightness setting and set the brightness at its minimum. Setting a shorter screen Time Out
is useful too

3. Disable Unnecessary Home screen Widgets.  Disable Live Wallpapers
4. Turn off auto Sync , Disable Background Data.
5. Use a Task Manger to close the entire Unnecessary
open Apps

6. Try to disable Vibration and Haptic feedback
I know these tips are very simple but trust me friends, they are quite effective. Thanks for reading, Enjoy!