Check local snowfall records. According to Lowe's, two-stage blowers are appropriate for regular snowfall of 8 to 12 inches or more. Electric and single-stage machines may be an option if your regular snowfall measures 8 inches or less, and if you clear only flat surfaces.
Determine how strong you are and how much time you have. Those two-stage, 250-pound monsters will blitz through a ton of snow, but they're heavy and often tricky to steer. If you're strength-challenged, go for a smaller model that's easier to control. If getting a large job done quickly is your priority, however, opt for a larger two-stage model with a wide clearing path.
Measure your driveway. Your new snow blower should be able to throw snow at least that far and ideally a little farther because wet snow often doesn't travel as far as the blower's advertised maximum throw distance. This also gives you an idea of how long an extension cord you need for an electric model; estimate generously because the extra length will come in handy. David Beaulieu, About.com's guide to landscaping, warns that electric snow blowers are only suitable for driveways less than 150 feet long. (Note: ConsumerSearch is owned by About.com, but the two don't share an editorial affiliation.)
Measure your walkway and any other surfaces you'll use the blower to clear. There's no point in buying a massive 28-inch-wide snow blower if you need to clear just a narrow walkway or a back deck.
Measure where you plan to store the snow blower. You can always shuffle things around later, but having at least a rough idea of how wide and deep the space is will keep you from buying a machine that's too big to store properly.