There are two parts to your laptop that will drain the battery the quickest: the display and the hard drive.

To increase your battery life follow the steps below.

First you should calibrate the battery.

In your energy preferences you should set your monitor to sleep when not in use.

Disconnect any devices that are plugged in via USB or Firewire.

Quit Applications that are not in use.

Remove any CD or DVD that is not needed.

Reduce the brightness of the display.

If you are not using Airport, turn it off.

If you have BlueTooth installed and are not using it, turn it off.