The weight of you and whatever gear you plan on hiking with is often the most important. The overall purpose of a snowshoe is to keep you afloat on the snow, and if you choose the wrong size for your weight, you will be back to breaking through the snow and having to trudge through thigh deep snow with feet three times their normal size. Most snowshoes will have a weight range listed on the tag, but they are often a huge spread. You want to choose the smallest size that fits your weight requirements. This helps minimize the weight of the snowshoe themselves. Typical sizing from manufacturers are in lengths of 25" (up to 200 lbs.), 30" (up to 250 lbs.), and 36" (up to 300 lbs.).
Terrain is important when looking at the components of the snowshoe. If you will be using them on flat ground you can often get by with simpler binding systems and less traction enhancement. Rolling hills are the next step up and may require a stronger binding system to keep your foot snug and a beefier heel and toe crampon for traction. And, if you are planning on any steep hills or mountain snowshoeing, look for a snowshoe with aggressive traction enhancers to keep you from sliding off the mountain and a heel lift that helps with calf strain on steep surfaces.
And finally, the snow conditions are also something to address. Deep powder requires a larger surface area to distribute your weight effectively, while packed trails could be navigated with a smaller lighter frame. If you will be using your shoes on packed trails most of the time and may occasionally use them in powder, some manufacturers offer a floatation add-on to your snowshoes to give you more surface area in that situation.
I hope to see more people out on the trails this winter trying out their new snowshoes.