Wiring outlets and switches is at the heart of home electrical wiring. You can modify your home wiring to accommodate extra switches or outlets by connecting them together through a process known as piggybacking. Piggybacking simply involves tapping into the wires leading to or from one device, like a switch, and connecting to another, like an outlet.
Turn off the power to the circuit you'll be working on at the source, the breaker box. Never work on a live electrical circuit.
Remove the cover for the switch. Most switch plates are held in place with two screws, one at the top and one at the bottom. Remove these by turning them to the left with a flat-bladed screwdriver, then pull the cover off.
Remove the screws holding the switch in place in the gang box. There will be two of these, one at the top and one at the bottom of the switch. Turn them to the left with a flat-bladed screwdriver to remove.
Pull the switch out of the gang box as far as possible. Cut the portion of the cable attached to the switch that you'll be tapping into for your piggyback connection.
Remove 1 inch of insulation from either side of the cut you've made in the cable, using a sharp knife. Then remove 1/2 inch of insulation from the black and white wires revealed in the cable, using a set of wire strippers.
Prepare the end of the cable that's attached to your outlet by removing 1 inch of the cable's outer jacket with a knife, and then taking 1/2 inch of insulation off of the individual black and white wires with a set of wire strippers.
Hold the bare ends of the three white wires together, slip a wire nut over the end, and twist it until the wires are securely fastened together. Do the same for the black wires and you've completed piggybacking the outlet to your switch. Replace the wiring in the gang box, replace the switch and cover and turn the power back on.
Never work on a live electrical circuit.