1. Dim the screen brightness or use auto brightness.
2. Keep the screen timeout short, I have mine set to 30 seconds
3. Only turn on Bluetooth when you need it
4. Only turn on Wi-Fi when you need to use it
5. Turn off non-essential notifications
And the final tip is something that gave a big improvement on my Andriod phone, and I have been told that it also work for iPhones. Uninstall the Facebook app and access Facebook using the Browser. You get the same functionality, with a lower drain on your battery.
If you have any more tips, why not post a comment on this blog.