This information is reprinted from a Department of Public Safety bulletin. 

Tips for homeowners in removing snow and ice from roofs and other areas:

1. Use a snow rake for pitched roofs (available at most hardware stores) to remove snow from your roof.
2. Start from the edge and work your way into the roof.
3. Try to shave the snow down to a 2 or 3 inches on the roof instead of scraping the roof clean, which will risk damage to your shingles or other roof covering.
4. Keep in mind that any metal tool could conduct electricity if it touches a power line. Also, metal tools will do more damage to your roof.
5. Shovel snow from flat roofs throwing the snow over the side away from the building. 
6. Most plastic shovels are better, except for the ones with curved blades—those too will do some damage to your roof.
7. Remove large icicles carefully if they're hanging over doorways and walkways.  Consider knocking down icicles through windows using a broom stick.
8. Wear protective headgear and goggles when performing any of these tasks.
9. Consider hiring professionals to do the job. The combination of heights plus ice makes this one of the more dangerous house chores.
10. If you don't hire professionals, at least have someone outside with you in case anything does go wrong.
11. Keep gutters, and drains clean, free of ice and snow and keep downspouts clean at ground level.

The state Department of Public Safety also advises: 

• Unless approved by a registered professional engineer, don’t add your weight or the weight of equipment to the roof.
• Don’t use a ladder since ice tends to build up on both the rungs of the ladder and the soles of your boots.
• Don’t use electric heating devices like hair dryers or heat guns to remove snow and ice.
• Don’t use open-flame devices to remove snow and ice.