Dim your screen - Most laptops come with the ability to dim your laptop screen. Some even come with ways to modify CPU and cooling performance. Cut them down to the lowest level you can tolerate to squeeze out some extra battery juice.

Cut down on programs running in the background. Itunes, Desktop Search, etc. All these add to the CPU load and cut down battery life. Shut down everything that isn’t crucial when you’re on battery.

Cut down external devices - USB devices (including your mouse) & WiFi drain down your laptop battery. Remove or shut them down when not in use. It goes without saying that charging other devices (like your iPod) with your laptop when on battery is a surefire way of quickly wiping out the charge on your laptop battery.

Add more RAM - This will allow you to process more with the memory your laptop has, rather than relying on virtual memory. Virtual memory results in hard drive use, and is much less power efficient. Note that adding more RAM will consume more energy, so this is most applicable if you do need to run memory intensive programs which actually require heavy usage of virtual memory.

Run off a hard drive rather than CD/DVD - As power consuming as hard drives are, CD and DVD drives are worse. Even having one in the drive can be power consuming.

You can even use programs like Microsoft's Virtual CD ROM program to make a file to use like a virtual CD.

http://www.softwarepatch.com/windows/xpvirtualcd.html

Keep the battery contacts clean: Clean your battery’s metal contacts every couple of months with a cloth moistened with rubbing alcohol. This keeps the transfer of power from your battery more efficient.

Take care of your battery - Exercise the Battery. Do not leave a charged battery dormant for long periods of time. Once charged, you should at least use the battery at least once every two to three weeks. Also, do not let a Li-On battery completely discharge. (Discharing is only for older batteries with memory effects)

Hibernate not standby - Although placing a laptop in standby mode saves some power and you can instantly resume where you left off, it doesn’t save anywhere as much power as the hibernate function does. Hibernating a PC will actually save your PC’s state as it is, and completely shut itself down.

Keep operating temperature down - Your laptop operates more efficiently when it’s cooler. Clean out your air vents with a cloth or keyboard cleaner.

Set up and optimize your power options - Go to ‘Power Options’ in your windows control panel and set it up so that power usage is optimized (Select the ‘max battery’ for maximum effect).

Don’t multitask - Do one thing at a time when you’re on battery. Rather than working on a spreadsheet, letting your email client run in the background and listening to your latest set of MP3’s, set your mind to one thing only. If you don’t you’ll only drain out your batteries before anything gets completed!

Go easy on the PC demands - The more you demand from your PC. Passive activities like email and word processing consume much less power than gaming or playing a DVD. If you’re got a single battery charge - pick your priorities wisely.

Get yourself a more efficient laptop - Laptops are getting more and more efficient in nature to the point where some manufacturers are talking about all day long batteries. Picking up a newer more efficient laptop to replace an aging one is usually a quick fix

Turn off the autosave function. MS-Word or Excel’s autosave functions are great but because they keep saving regular intervals, they work your hard driver harder than it may have to. If you plan to do this, you may want to turn it back on as the battery runs low. While it saves battery life in the beginning, you will want to make sure your work is saved when your battery dies.