If the battery life on your Android device could be better, here's a few general tips that may help. The following list was compiled with Android 4.0+ in mind, but may prove useful for older (or even future) versions of the operating system.
Turn off WiFi, Bluetooth, GPS, NFC, Location, and other services (e.g. Samsung's Air Gesture, Air View, & Smart Scroll) when not in use
If your device has a power saving mode, turn this on - this may reduce CPU speed and make the device a little slower, so remember to turn it off again when no longer required
Set the display to the minimum acceptable brightness, and consider turning off auto brightness (Auto brightness may need to be turned off to adjust brightness at all, depending on model/manufacturer)
Use a white background to save a little power on devices with LCD displays, e.g. HTC One, and a black background to save a little power on devices with OLED displays, e.g. Samsung Galaxy S devices
Under Settings/Data Usage, you can turn off background data on a per-app basis
Consider using a poll schedule instead of push for email accounts
Disable sync for unneeded accounts and services, e.g. Google+, Google Newsstand, Books, Movies, Music, or Picasa Web Albums
Disable automatic updates for apps from within the Play Store settings
Disable search for unneeded apps & data within the Google Search app
If your battery life has taken a dive recently, check out your most recently installed apps & see if uninstalling them helps
Take a look under Settings>Applications>Running to see if anything is running in the background when it shouldn't be
If you have no joy with all of the above, try backing up data & factory resetting - In addition to Google's data backup, manufacturers such as Sony and Samsung offer desktop backup software that can be used to restore data after a factory reset
If this helped, or you have any additional suggestions, please do sing out!