Go into the Settings, tap on Display, turn off Auto Brightness and then set the brightness that you want. You can comfortably get by on some of the lower settings.
Reduce some of the connections your phone is making. Every time your Galaxy S3 searches for a Wi-Fi network or seeks for GPS, that eats up battery life. This is especially important in areas where there isn’t a stable connection or the GPS signal is weak. In places like this your device will keep searching for a nearby Wi-Fi or GPS signal. This drains the battery very quickly. If you know that you’re not going to need either of these, go into the Settings and turn off Wi-Fi and GPS. You’ll have to manually turn these on when you want to use it, but Samsung made this super simple to do by including quick access to these in the Android notification bar.
Make sure you know which apps have access to your phone’s location features and adjust accordingly. For something like Foursquare or Google Maps, having location capabilities is a must but you should think about whether other apps really need to know where you are.
Turn off background data syncing. For those who need every single Tweet, email or Facebook notification in real-time, turning off background data may seem crazy but it definitely will save on battery life.
You can download JuiceDefender Ultimate or JuiceDefender to help monitor your Android’s battery.
Make sure to charge your smartphone often and don’t let your battery drain completely before you decide to plug it into the charger. Try not to let it get below 10 percent too often. Once per month you can let it completely die. This is called power cycling, and it is important to the health of a battery.
Keep your smartphone at or close to room temperature. Don’t put it in the sun.