The Martha Stewart Show, February 2011
Shut off fuse to light switch at circuit breaker.
Unscrew and remove light switch faceplate. Test for power using a circuit tester, and continue only if the tester does not light up.
Disconnect wires from old switch, noting which wire is the ground wire. Strip insulation off the wires to expose more wire for a better connection, if needed.
Using wire twisters included in dimmer packaging, connect wires to dimmer switch by connecting the house wires to the house connection and the ground wires to the ground connectors. Tuck wires into light box.
Attach dimmer switch by screwing it to the switch box in the wall. Attach new dimmer switch face plate.
Turn fuse back on at circuit breaker, and set dimmer to preferred lighting.
Before shopping for a dimmer, determine if you need a single-pole or three-way switch: A single-pole switch controls only one outlet or built-in fixture from one location; three-way switches are used when you have two switches that operate one light. To make sure your dimmer can handle the necessary wattage, calculate the total in your light fixture by adding up each bulb wattage. (For example, four 60-watt bulbs in one light fixture mean the wattage for that fixture is 240.)