When you're adding a new light and switch or connecting new outlets to existing ones in a finished room, you have to pass wires laterally behind the wall. That's easy to do before the drywall is installed -- all the electrician has to do is drill holes in the studs and snake the wires through. If you want to do that in a finished home, however, you have to remove the drywall, which is a messy and expensive job. An easier way to feed the wires is to snake them into the attic or basement, assuming you have access.
Attic or Basement Available
Find the intersection of the wall plate in the attic or basement. If the attic floor is unfinished, you should be able to see the plate from above with a flashlight. To find the point where the bottom plate intersects the floor joists, you may have to take measurements of the wall's position relative to the outside wall with a tape measure.
Locate the stud you're affixing the new electrical device to, and drill a 3/4-inch hole in the wall plate next to it. If you haven't done it already, cut a hole in the drywall for the electrical box for the new device, using a drywall saw.
Feed the cable vertically through the hole to the box. You may need to station a helper near the hole to catch the cable. It helps to straighten out a coat hanger, tape the cable to it and feed the coat hanger through the hole. The stiff coat hanger wire is easier to manipulate and catch than electrical cable. You can also use fish tape, a coil of semi-rigid wire used to feed electrical cables through walls.
Drill holes for all the devices you're connecting to the circuit in the same way. Feed the cables to them and run the cables laterally through the attic or basement to their points of connection, which is usually the main panel. Staple the cables to joists or rafters with wire staples.
Attic or Basement Not Available
Plot the path of the cable from its point of connection to the device it will power along a wall or ceiling. Locate all the studs or rafters along the path with a stud finder. Mark the stud locations with a pencil.
Cut a 4-by-4-inch rectangular hole in the drywall in front of each stud or rafter with a utility knife and drywall saw. Remove the drywall carefully so you can use it to patch the hole.
Chisel a notch in each stud or rafter that is about 1 inch long and 1 inch deep.
Attach the cable to fish tape. Feed the fish tape through the hole for the electrical box at the cable's point of connection and catch it at the first stud or rafter. Feed it from there to the next stud and rafter, continuing in this way to the cable's point of use.
Cover each notch with a protective metal plate. You can buy these plates at hardware stores. They have barbs that act as nails to hold them to the wood.
Fill each hole in the drywall with the piece you removed, screwing it to the stud above or below the plate. Tape and finish the patches with drywall tape and joint compound.