The parallax feature on iOS 7 makes any wallpaper you choose gently roll left or right, as you tilt the device one way or the other. The gimmick offers an interesting 3-D effect, not unlike the kind offered by the lenticular 3-D postcards of the 70s. The special effect, though, comes at a cost -- it uses battery power-intensive sensors such as the gyroscope and the accelerometer a lot. To turn off parallax to save on battery power, you need to go to Settings | General | Accessibility and turn on the Reduce Motion feature.
By default, iOS 7 leaves Bluetooth turned on. For their part, users tend to leave Wi-Fi and AirDrop turned on. If these are features that you aren't actually using, you waste power on keeping them turned on. This is why iOS 7 makes it easy to turn them off and on whenever you need to -- you simply need to bring up the Control Center by dragging up from the very bottom of any screen, and tapping the buttons for Bluetooth, AirDrop or Wi-Fi.
Many apps try to tap into your GPS location even when there isn't much benefit to be had. The more apps you have that use your device's GPS, the more battery power you waste. There's an easy way to deny GPS access to apps that don't need it, though. All you need to do is to go to Location Services under Settings and Privacy . You'll see every app with access to GPS Location Services on the list that shows up. You get to toggle off everything that you believe doesn't need GPS.
The auto-brightness feature in iOS 7 is intended to help keep the screen at a comfortable level of brightness. Unfortunately, it tends to crank the brightness too high. You end up burning more battery power than you have to. Turning off auto-brightness (Settings | General | Wallpapers | Brightness) and turning the brightness slider down manually isn't much of a sacrifice.
A lingering press of the home button is the default way to turn on Apple's speech recognizing assistant Siri. Since pressing the button can be a chore, though, iOS 7 allows you to turn on Siri simply by raising your phone to your ear. The feature is called Raise to Speak . Since it uses substantial battery power, turning it off can be a good idea.
When you set your email to Push , your email provider will send you new email as soon as it appears -- one by one. With Push running, then, your device will need to burn battery power getting on the Internet and receiving email individually. If you don't have high-priority mail that you look forward to all the time, though, it's a better idea to have your phone go out and look for email at set intervals ( Settings | Mail | Contacts and Calendar | Fetch New Data) . Since downloading multiple emails takes no more time than downloading just one, you'll save energy.