I've had good luck sometime by using a Park pedal wrench (the one with two slots at different angles) and picking the point where it creates a narrow angle between the wrench and the crank. Hold the opposite pedal and apply force to the wrench. This way you are pulling back toward the crank axis rather than extending the effective length of the crank making hit harder to keep the crank from rotating, thus wasting energy. Reduced chance of busting knuckles this way as well.