As people said you want to be as close to the road as possible. Wider tires are great for dry traction, but for snow you don't want to be "on top of the snow" you want to cut through it. Like wider tires during a rain storm. You will hydroplane easier.

You want as skinny tire as possible when it snows. And as much siping as you can get on the snow tire. Siping helps so the tire has as much grippy "fingers" grasping at the road and also helps to keep the tire clean from debris. Also deeper treads help too so snow doesn't gather in the tread and cause you to loose more traction.

So my Civic Si comes with 195/55x15" I would actually get 185/65x15" snow tires.