Shovel as much snow off the ice as possible. Removing snow from an ice layer allows faster melt, especially if the porch receives sunlight. De-icing compounds will also act more efficiently.
Apply a de-icing compound evenly across the icy porch surface. There are several possible compounds that can be used for this. Sodium chloride, or rock salt, is a traditional and inexpensive de-icer but is corrosive and may damage vegetation and the porch surface. Salt-free de-icers that contain calcium magnesium acetate are more expensive but will generally be less damaging to the porch material and nearby plants.
Shovel the area again once the de-icer has broken up the ice enough for manual removal. If patches of ice remain, sprinkle as little de-icer as necessary on those areas.