Disabling Push Email will let your device idle rather than constantly waiting around for a new message. Sure, you might not get an email seconds after it was sent, but if immediate delivery isn’t critical you should just set your phone to poll your mail servers less often.
Turning off Location Services is another helpful battery saver. Your GPS loves sipping power, so if you keep your apps from constantly tracking your location your iPhone will last a bit longer.
Download over Wi-Fi instead of LTE or 3G. If you have any larger downloads, such as a software update, a podcast, music, video, or whatever, you’ll be better off letting Wi-Fi handle the download. First of all, it’ll generally download faster over a Wi-Fi connection so your phone won’t be actively downloading for quite as long. Second, your phone’s LTE and 3G radio tends to be a little more battery-hungry so it’ll cause more of a drain regardless.
Disable unnecessary notifications. Every time you receive a notification, your device’s screen lights up to tell you. This takes a little power and you probably don’t need to be notified of every little thing that every app wants to tell you. Go into your iPhone’s notification settings (in the Settings app) and turn off notifications for any app you don’t really care about.
Buy plenty of extra chargers so you can power your phone wherever you are. This doesn’t necessarily improve your battery life but it improves the likelihood that your iPhone will last as long as you need it. Put a charger in your car, at your desk, by your bed, and anywhere else you frequently find yourself so you never have to go through any trouble to plug it in.