Weight and size
Weight: Most laptops weigh between 1 - 2 kgs. (Some heavier, some even lighter!) When you're buying your laptop, ask yourself if you'll be taking it outside your house often. If the answer is yes, you'll want to buy a thinner, lighter laptop that will fit into your bag or briefcase.

On the other hand, if your laptop is going to stay in your room most of the time, you might want to consider investing in a laptop that has more features; it'll be bulkier, but it will be packed with each and everything you need.

Size: The most common screen sizes on laptops are 12.1, 13.3, and 14.4 inches (although some really tiny laptops have screens that are as small as 8.4 inches). Again, a tiny screen is appropriate for frequent travelers, but it'd be ideal to have a larger screen if it’s convenient and you do not have to move around much.

Input devices
Instead of a hand-driven mouse, laptops come with other more cumbersome "input devices" for navigating a cursor around the screen. You have to get used to them. Hard-core gaming with these devices might be a little problematic. The kinds of devices that come with laptops are:

Touchpad: A touchpad is a square-shaped surface located below the space bar of a laptop keyboard. It is touch-sensitive and you navigate the screen by moving your finger around the box, as if you were drawing. The majority of laptops have a touchpad as their input device. A touchpad can be a bit tough to get used to (you have to be careful not to let your thumb fall on it while typing, or it'll move the cursor), but they work quite nicely.

Pointing stick or rubberized nipple: This input device is a tiny rubber dot that sticks out of the keyboard right between the G, H, and B keys, and it responds to pressure from your index finger. So you navigate the cursor by applying pressure in the direction you want the arrow to go (like a joystick). Sounds easy, but most people find nipples very frustrating to use - the slightest touch causes the arrow to go flying across the screen. However, I love the nipple. My laptop's red nipple has helped to make all the great pages of indiahowto.com so far.

Batteries
Batteries act like your laptops in-built UPS (Un-interrupted power supply!). You can charge your laptop and then you don’t need a plug point to use it. It will run on battery for a few hours. However, it is important that you check up how many hours your battery will run. Some batteries last long. Some don’t. You want a battery that lasts the longest and is still in your budget!

There are three main types of batteries:

Li+: Most people get Lithium-ion (Li+) batteries. These batteries range in quality; batteries with a high milliampere and high voltage measurements are best. These are generally good, safe and secure.

NiMH: If you want something cheap, a nickel metal-hydride (NiMH) battery will do. However, be aware that they'll require you to recharge them every hour or so.

NiCad: This probably won't be an option, but if a dealer does try to sell you a nickel cadmium (NiCad) battery, run away. NiCads are the worst batteries because of their requirements for constant recharging.

However, all this may not be true in the near future. Technology is changing. Things are getting better. So, if you are reading all this many years after it has been published, you might want to check up on the latest developments in the battery world.

Display
There are two types of displays (that is, screen images) to choose between: active-matrix (a.k.a. thin-film transistor or TFT) and passive-matrix (or dual-scan).

Active-Matrix (TFT): Go for an active-matrix display if you've got enough cash. It'll be worth it. Pictures come out sharper and moving images play out smoother. In fact, nowadays most laptops come with active-matrix displays because they're so commonly preferred.

Passive-Matrix (Dual-Scan): This is the older and cheaper display. Images that run on this display react more slowly. It's not a that great, but it’s cheap. If you need a laptop purely for word processing, or excel or accounts, this kind of display should be good enough. If you want your laptop for hard-core gamming and making 3d animations, then this may not be a good idea.

To figure out what type of display you're dealing with on a laptop, move the cursor very quickly across the screen. If the cursor disappears while moving, the display is passive-matrix, and if you can keep your eye on it, it's active.

Other things to look out for:
Keyboard: All laptops have cramped keyboards, but at least try to find a laptop with a keyboard with which you can comfortably type. Also, consider getting a spill-resistant keyboard if you have kids or work in a “spill” type environment.

Durability: If you plan on taking your laptop just about everywhere, you might want to consider a model with shock-resistant hard drive mounts. These are specifically designed to protect your laptop from bumpy rides and crashes.

Your Compatibility: If possible, “test-drive” a laptop before purchasing it. A laptop is different from a computer. In a computer if you don’t like your mouse or cd-rom drive you can replace it. In a laptop that is not possible. Once you buy it, you either keep the complete piece or you throw away the complete piece. (Please don’t throw it away. Give it to me!) It is hard to replace an annoying keyboard, an irritating touch pad device, or a poor display. So make sure that you're okay with your laptop by playing around with it.