The single tactic that worked best was air-sealing the attic floor before touching the roof. Ice dams usually start because warm air leaks into the attic and melts snow from below, not because the roof is defective.
What we did was seal top plates, light fixtures, and attic access gaps with fire-rated foam, then added insulation baffles to keep soffit vents clear. Overlooked detail: do this before the first heavy snowfall, not mid-winter. Once snow loads the roof, heat patterns are already set and fixes are less effective. After sealing, roof temps evened out and ice dams stopped forming without heat cables or shingle damage.
Albert Richer, Founder, WhatAreTheBest.com