1. The first thing you should do is check which apps are using up your battery:
2. Only allow certain apps to use data unless you're on Wi-Fi:
3. Absolutely make sure you turn off Wi-Fi assist:
4. When you're not using your phone, turn it face down and it won't light up when you receive notifications.
5. Turn off auto-brightness:
6. Turn on "Reduce Motion" to stop your phone from animating.
7. If you're running low on power, turn on Grayscale to save even more battery.
8. If you have bad or no service, consider turning on Airplane Mode so your phone won't constantly search for a signal.
9. Stop your email from automatically pushing to your phone.
10. If you really get desperate, turn off notifications.
Start in Settings > Notifications, once inside Notifications, tap on all the apps you want to turn off notifications for.
11. Take off your case when charging.
12. Decrease the time for Auto Lock.
13. A Wi-Fi connection uses less power than a cellular network, so make sure to keep Wi-Fi on at all times.
14. Turn off Location Services.
To turn off Location Services head to Settings then Privacy and then Location Services and either turn off Location Services altogether, or deselect any apps that you don't need to access your GPS.
15. Disable Background App Refresh:
Head to settings then General and finally Background App Refresh and turn it off all the way or turn it off for individual apps.
*Background App Refresh pre-loads apps in the background keeping them constantly updated even when you're not using them. If you don't need a specific app to always keep updating (like a game or Facebook for example, turn it off).
16. Turn off automatic app updates:
Start in Settings > iTunes & App Store and turn off all of the automatic downloads. If you want to take things an extra step, turn off Suggested Apps too.
*Always make sure that your iPhone is updated to the latest software to get the best battery life too.