Where do I need to insulate my house to help avoid ice dams?
Ice damns are caused by heat rising to the underside of the roof, heated it and melting the snow, where it refreezes as ice.

You need to make sure no hot air is leaving your house - insulate thoroughly.

Airflow is also crucial - make sure you leave baffles to provide airflow from the eaves to every part of the attic. If you have a "one and a half" or similar you need to provide that channel of air between the corner (of roof) crawl spaces and the proper attic.

A well ventilated attic, with no heat bleeding into it, will not ice dam!