Your primary intended use for a laptop computer is the most important consideration when deciding on which one to purchase. If it's mainly for home use, you don't really need to be too concerned with size, weight and battery life; a conventional laptop will be just fine.
Look for features that make the laptop a satisfactory alternative to a desktop: fast processor speed, a generous amount of RAM, a large bright display, and lots of peripheral ports or a docking station that lets you hook up printers, extra monitors and other accessories, but still enables you to move the computer easily.
On the other hand, if you're going to be travelling with the laptop, or will be carrying it in and out of your car multiple times during the day, then you should focus on long battery life, rugged construction, and an exceptional ability to establish wireless Internet connections. This is where compact laptops, sub-notebooks and netbooks become attractive options.
Take some time to see what's out there. Look at ads and listings online and in catalogs to get a feel for price ranges. You'll notice that over time, the price of a laptop computer remains pretty constant, but the capabilities of the computer keep expanding.
If you have a good idea of what you want, you'll be ready to pounce when you see a loss leader price, or you'll find the sweet spot between the phasing out of a product line and the rolling out of the new models. Then you'll be able to grab the top dog from six months ago for anywhere from 20 to 50 percent less than it used to cost.
The late summer, just before school starts up again, is a prime time to find bargains; another is the winter holiday season. These are great times to use the intense competition in the computer market to your advantage.
Unless you are getting coverage for accidental damage, don't throw money away on an extended warranty. Any reputable manufacturer is going to give you a one-year warranty anyway, and you can double this by using certain credit cards. If a computer is going to have issues, they will most certainly occur well within this time frame, and given the rapidity with which computer technology evolves, in two years you'll probably be ready for a new laptop, and you'll still have a perfectly good one to use as a backup.