Mmm.. depends what you are using it for. In general, assuming you are using Win 7 or so, keep the power saving options on and leave it on the balanced profile or whatever and tailor it to conserve energy or dim/shut down the monitor after a short time of non use. Play around with the power options, you can set different power profiles for when it's running on the battery and when it's plugged into A/C power. Have the screen dim after like 30 seconds or something on battery... bright screen eats a lot of power. Having the laptop hibernate instead of sleep will also conserve the battery more.
Don't have shittons of background apps / resource hog programs, turn off/remove any non-essential programs.
Turn off WiFi when not being used as that will eat up power. Defrag regularly. Keep the system cool.
Charge the system regularly. Lithium Ion batteries are good but don't do well being fully discharged.
