Generally, they recommend that every time you run the laptop on battery you let it run to as close to 0 as possible. It is also recommended that if you leave your laptop plugged in for extended periods of time, that you remove the battery from the system. Your laptop can run without the battery and leaving the battery in while on the charger can shorten it's life. Trust me on that one, it happened to my laptop
Check the manual for your laptop, too. They usually have some suggestions to help save the battery.