More in Electrical
The most important step when doing any electrical work is to make sure the power to the circuit is turned off. Shut off the power at the circuit breaker or fuse box. Also, double check that the power is really turned off by flipping the switch on and off to make sure the current is really off to make sure there is no flowing current flowing through the line.
Once the power is off, remove the existing switch plate using a screwdriver.
Remove the screws that keep the switch attached to the box.
Disconnect existing wiring from the box and remove the box (always unscrew the grounding wire last).
There will be three wires: one black, one white, and a separate ground wire that may be bare copper or sometimes wrapped in green. Identify the three different colored wires and attach the dimmer with the wires in the same manner. Connect the black wire to the black wire, etc. Use pliers to gently twist the ends of the wires together and then secure them together with a wire nut until it is tight and won't turn anymore.
Carefully push the wires back into the electrical box.
Screw the new dimmer switch to the electrical box and then replace the cover plate.