Dim the screen: Adjust your brightness by dimming the screen as much as you reasonably can. A dim screen will help maximize your laptop's battery life, but make sure that you can still comfortably see your display.
Minimize unneeded apps and options: Turn off AirPort and Bluetooth when youre not using them, and make sure that you dont have any programs running in the background: Quit all apps, disconnect peripherals, and eject discs from your disc drive if youre not using them.
Opt for battery-saving apps
For your MacBook or MacBook Air, you can use a battery-monitoring app to keep closer track of your energy supply. Some of these apps, such as Low Battery Saver, let you customize your Macs battery warnings. That way, youll have a better (and more useful) idea of how much battery life remains.
DeepSleep is another handy app that causes your MacBook to hibernate instead of just putting it to sleep when you close the lid while its still powered on. (Even in sleep mode, your Mac draws power from the battery.) DeepSleep saves the contents of RAM to your hard drive and stops drawing any power from the battery when your MacBook is not in use. Your Mac will wake up from hibernation a bit more slowly; but when it does, all of your apps and documents will be restored to exactly the state you left them in, and your battery will be less taxed.
[Editors note: This story was updated on 11/16/2012 for iOS 6 and Mountain Lion compatibility, as well as to include new Apple devices.]