Make sure your roof is peaked. This helps keep the snow off your roof because the snow is able to slide off instead of accumulate like it would on a flat roof. Most roofs in snow-prone areas are designed with peaks.
Keep your roof free from leaves and branches. These items prevent the snow from sliding off causing it to build up. Keeping your trees trimmed away from your house will help prevent the branches and leaves from falling on your roof.
Take off your rain gutter during the snow season. It collects snow down in the gutter which compiles over time. This creates a ledge on your roof allowing the snow to pile up behind it instead of being able to slide off the roof.
Rake the snow off your roof every day. You can buy a snow rake with an extended handle making it easy to just rake the snow off your roof before going to work. Check out vermontcountrystore.com for a 16-foot snow rake to help keep your roof clear.
Use a snow guard. These install on your roof and blend in well with the rest of your house. A snow guard melts the snow on your roof preventing it from building up. They're available at snoblox-snowjax.com.