To make sure you are getting the most out of your iPhone's battery, make sure you frequently close apps that you aren't using.
To do this, double tap the home button. Then, swipe up to close the apps that are currently running. You may be surprised how many you have left open that you aren't aware of.
This is a common practice that should be done regularly throughtout the day to increase the overall lifespan of your battery.
To identify what apps are using the most of your battery life on your particular phone, go to:
From here, you can view the apps that have used the most of your battery for the past 24 hours, as well as the last two days.
For me, Facebook has been using the most activity. The Facebook app is known to be a huge battery drain, so it's best to limit the time on the app itself. Using Facebook in safari is a good alternative.
While you were checking your battery usage, you may have noticed some apps stated "Background Activity." This means the app is running in the background when you aren't using it. To minimize this, go to:
Settings>General>Background App Refresh, and turn off the feature. This will keep the apps from updating in the background.
When you checked your battery usage in Settings>Battery, if you scrolled to the bottom and found that your "Usage" time and your "Standby" time were the same, your iPhone is never going into Standby mode, even if you've locked it.
This has happened to me before, and the best way to fix the problem is to do a normal restart by turning your phone off and then on. If the problem persists and your phone is up todate software wise, a trip to the Apple Genius Bar is in order.