Before thawing a frozen pipe, make sure it is not cracked. If it is, turn off the water and repair the break. To thaw a plastic pipe, wrap it with rags and pour boiling water over it.
Use the same method for metal pipes or, after opening the nearest faucet, use a heat lamp, hairdryer, or propane torch to warm the pipe gradually, working backward from the faucet toward the frozen area. Never let a pipe get too hot to touch. Keep metal pipes (not plastic ones) from freezing by wrapping with electric heating cable and insulation.
During a winter cold snap, open all faucets a little. A steady drip may be enough to keep the water from freezing, and even if it does freeze, the open line may save the pipes from bursting.