There are several methods of thawing frozen pipes. Some of these methods depend on the specific type of pipe that needs thawing. First, open all faucets unless you suspect cracked pipes (See tip below for cracked pipes). If you have plastic, PVC pipes, or metal, you can wrap them with cloth material like rags and pour boiling water over the cloth. The cloth will absorb the hot water keeping it against the pipe. You may have to repeat the process several times and work your way along the pipe. It's best to start from the faucet and work backwards. A hair dryer can also be used to heat pipes. You can also use a blow torch to carefully and gradually heat metal pipes only and not PVC. See warning below if using a torch.
Warning if using a torch to thaw frozen pipes: Open flames can start a fire near types of insulation, wood beams, and near other combustible structural areas. Use extreme caution. Never use a torch near gas lines or near flammable liquids. It's advisable to use boiling water or a hair dryer since these are safer methods and may work just as well.
Tip: If you suspect freezing has cracked your pipes then turn off the main water source before thawing pipes and repair the cracks.