Different specs are important to different people, but a few generalizations hold true for most cameras.
If your intentions to take pictures only to e-mail or to upload to social-networking sites, a camera of any resolution will do. Although, having more pixels gives you greater flexibility - you can print sharper pictures at larger sizes or crop and print small sections of pictures. These days, it's hard to find a camera with a resolution of less than 10 megapixels, which is overkill for most shooters. As a rule of thumb, 5 megapixel is enough to make a sharpe 8x10 inch print; and 8 megapixels is enough to make a sharp 11x14 inch print. A 10 megapixels camera can produce acceptable prints of up to 13x19 inch, although they may lose some details. Images from 13 megapixel camera look good at 13x19 inches and can be pushed to 16x24 inches. Many digital single-lens reflex (DSLR) cameras today offer 16 megepixels sensors.
Cameras with larger sensors and lenses normally take better shots regardless of the unit's megapixel count. Bigger sensors normally create better images, especially in low light, as do higher-quality lenses; this is why DSLRs take such stunning photos. In general, you pay more for a larger sensor.
If you can't get any hands-on time with a camera before deciding whether to buy it, check the specs to see how big its sensor is. It's not the only piece of hardware that factors into a cameras overall image quality, but it's usually a greater indicator of how good your photos will look.
Zoom lens and image stabiliztion
Inexpensive cameras often lack a powerful optical zoom lens, but that's changing. Among the new breed of $200-range cameras are a few pocket megazooms: compact cameras with optical zoom lenses as powerful as 10X optical zoom.
If we had to choose between a point-and-shoot camera with stronger optical zoom and one with higher resolution, we'd take the model with the more powerful zoom lens it means that you won't have to magnify your subject and then use software to crop the image (and discard some of the resolution as a result).
If you're buying a DSLR or a compact interchangeable-lens camera, both the zoom range and the stabilization features depend on the lens you're buying. A few DSLRs and interchangeable-lens compacts have in-body image stabilization, meaning that your images will be stabilized by in-camera mechanics (usually, the sensor physically moves to compensate for shake) regardless of which lens you attach. If your camera doesn't have in-camera stabilization features, you can obtain optically stabilized lenses, but they're a bit more expensive.
Fixed-lens cameras now offer zoom ratings beyond 40X. These lenses are great for nature or sports photography, but unless the camera has good image stabilization (look for a camera with optical image stabilization) or a very fast shutter, you may need a steady hand or a tripod to avoid blurry pictures at extreme telephoto lengths. Before you buy, you should try a camera's autofocus at full zoom: We've tested some models that were slow to focus at full zoom.
Also note that not all high-zoom cameras are created equal. You know how you have to ask everyone in your group shot to gather in close to get in the shot? A wide-angle lens can solve that problem, so pay attention to the wide-angle end (lowest number) of the optical zoom range, as well as to the telephoto end (highest number). If you take a lot of group shots or landscape shots, the wide-angle end of the lens is even more important; it lets you capture more of the scene when you're zoomed all the way out. A good wide-angle lens starts at about 28mm or less on the wide-angle end; the lower the number, the wider-angle the lens.
Be wary of advertised zoom ratings many vendors quote "extended zoom" or "simulated zoom" counts. These combine the optical zoom (which moves the lens to magnify the subject) with digital zoom, which merely magnifies your image digitally by cropping and zooming it. Optical zoom gives you all the benefit of the camera's maximum resolution, combined with the ability to focus in tight on faraway action.
Shutter lag and startup time
Even if the camera you've decided to buy has some drool-inducing specs, shutter lag may prevent you from capturing the perfect shot. When it comes to shutter lag, a camera can let you down in a handful of ways: a slow shot-to-shot time, a slow startup-to-first-shot time, and a laggy autofocus that has trouble locking in on a crisp shot.
You can check for only one of these problems by scanning a camera's spec sheet: To get a sense of a camera's shot-to-shot time, look for the camera's "burst mode" or "continuous shooting" count in shots per second. This is the number of shots a camera will take in rapid-fire succession as you hold the shutter button down. If you're interested in shooting a lot of sports or action photography, look for a camera with a continuous shooting mode of at least 3 shots per second
Bear in mind that a camera's listed continuous-shooting speed usually refers to situations where the flash is turned off and the focus and exposure are locked during the first image of the batch. Some higher-priced cameras have continuous autofocus enabled from shot to shot. Other cameras have very high continuous shot rates, but usually they significantly reduce the resolution of each photo in order to speed up image processing and write speeds.
The other forms of shutter lag are important reasons for you to get some hands-on time, if possible, with any camera before you buy it. Check to see how long the camera takes to power on and snap a first shot; generally, anything close to a second is considered fast. Another good hands-on, in-store test is to see how long the camera's autofocus system takes to lock in on a shot after you press the shutter button halfway down. If the camera searches in and out for more than a second, you'll be better off with another camera for sports or spur-of-the-moment casual shots.