Ensure that your insulation does not contact the roof deck, or block the soffit vents. Ensure that your upper roof area has adequte vents, and that they are not obstructed. Heater cables can help prevent ice damming, but if you're applying the cables after the snow and ice have already accumulated, place the cables only at the gutter, or lower-most portion of the eves. Higher placement may cause meltwater to accumulate behind an ice dam, worsening the situation. Also, ensure that you are not scraping the surface of your shingles.
Asphalt shingles are especially prone to damage by heavy foot-wear, and by shovelling or sweeping.
It is important that the gutters and downspouts are freely discharging meltwater. Ensure that downspout extensions are not frozen into the grass or soil. Home Reference Book by Carson Dunlop 1999-2000. Optimized for Netscape 4, Explorer 4 or better at 800x600 resolution.