What To Look For
When purchasing new binoculars, consider a number of factors, the most important of which is magnification. This is typically measured by two numbers, which will be described in the form A x B. A represents the number of times an image will be multiplied. If A were six, then the image would be appear six times larger through the viewfinder. B is a measurement of the diameter of the binocular lenses, which determines how much of the target space can be seen at once. Another important factor is a binocular's ability to focus, which can be anywhere from severely limiting to entirely customizable, with individual focus for each eyepiece. Finally, look for a measurement of brightness, which is usually determined by a measurement of the exit pupil. The larger the exit pupil, the more light is allowed in and the better the binoculars will be for low-light situations.
The most common mistake people make when purchasing binoculars is not adequately considering their needs. While maximum magnification may seem desirable, it also limits the user's ability to scan large swathes of sky, forest or water. Bird-watching is a perfect example of a need for balance between magnification and the necessity of scanning a broad sky for small figures. While larger diameter lenses and complex focusing systems may seem useful, they can add a lot of weight to a pair of binoculars, making them unsuitable for camping or backpacking.
Where To Buy
The best place to buy binoculars is at a sporting goods store that has employees that cater to your intended use. Grab a guy from the camping section to advise you if camping is your intended use. Do not buy binoculars online. Because binoculars are so variable and subjective, it is important to experiment with a pair before buying.
A good bargain pair of binoculars can be had for a little over $100. The most expensive can run up to $1,800. In general, the higher prices involve advanced optics and advanced accessories. Look to spend somewhere in between, with the sweet spot around $250.
There are a number of buyer's guides that compare specific models (see links below). In general, you will want to compare based on your needs and potential purchase's magnification. If you are looking to buy the binoculars for sporting events, then consider something with a wide view and low magnification, perhaps 6x35, as compared with the 8x30 useful for stargazing.
In addition to your binoculars you will want a carrying case and cleaning cloth. Optics are very sensitive to jostling and should therefore be treated as if they were very fragile. Additional accessories will often come bundled with the binoculars, such as digital rangefinders and compasses.
Try turning off the lights before testing your binoculars. This will give you a sense of the ability to view in low light conditions.