1- Update your device regularly; several updates improve  the use of the battery

2- Keep your iPhone in its “thermal comfort zone”, at temperatures between 0C and 35c (32 to 95F)

3- Pull out of the box when you charge it. Some cases overheat your device when it is connected and diminish its autonomy

4- If you are not going to use your iPhone for a long time charge half of the iphone; about 50% of its maximum charge. It is not recommended to charge it fully or nearly empty

5- Adjust the brightness of your device to “automatic adjustment” or as low as possible. High brightness will consume much more energy.

6- Always prefer a wireless network to a cellular network even if your are allowed several gigs per month. The iPhone uses less power on WiFi

7- Activate the “low power” mode now available with iOS9

8- Regularly check the percentage of battery use by applications running in the settings menu. This will let you know the percentage of battery used by each of your applications

9- Activate the “flight mode” when you are in a low reception area, so you prevent your iPhone to remain locked in signal search mode

10- When you upload from your computer, make sure it is plugged into a power outlet and that it is not in standby mode.

And here are three more:

11- Disable automatic updates of apps you do not use regularly

12- Disable automatic reception and email notifications

13- Disable location services, or activate them only when you need