Installing a garage door opener involves carpentry and mechanics as much as wiring. The wiring is about as simple as hooking up a doorbell. The power head usually plugs into an outlet, but check with your local building inspector to see whether it needs to be hardwired.
The carpentry and mechanics involve assembling a large piece of equipment and hanging it from the ceiling joists. It is a good idea to have a helper.
Garage door openers are available with screw-drive or chain-drive. A knowledgeable salesperson can help you choose the right opener. It helps to know what your door weighs, but you probably don't unless the door is brand-new and you still have the packaging. Instead, know the size of the door, what it's made of, and whether it's sectional or one-piece. You can take along a picture of it when you go shopping.
About 8 hours
Drill and bits, hammer, Phillips and slotted screwdrivers, tape measure, adjustable wrench, socket wrench, pliers, wire stripper, 6- or 7- foot stepladder
Wiring, basic assembly, minimal carpentry
The opener needs a nearby 120-volt outlet. The garage door should already be installed.
Garage door opener
The limit switches attach to the rail. One of them is adjusted later so it cuts off the motor when the door has closed. The other is adjusted to cut off the motor when the door is completely open. For now attach but don't adjust them. Run the limit switch wires to the power head and connect them.
Attach the bracket that supports the rail following the manufacturer's directions. Then support the power head on a ladder, box, or small table so that you can lean the rail assembly against its mounting bracket. Attach the rail to the bracket, tightening the screws or bolts finger-tight. Tighten them firmly once the power head is in place, or as directed by the manufacturer.
Attach mounting straps to the ceiling joists to hold the power head. The rail needs to be at a 90-degree angle to the door. If necessary, add framing so the straps are properly positioned. Hang the power head from the straps. For more on squaring up the rail, see "The 3-4-5 Method" below.
The 3-4-5 Method
Use the 3-4-5 method to make sure that the rail is square to the garage door. The method is based on geometry: If the sides of a triangle measure 3, 4, and 5 feet, the angle opposite the 5-foot side is 90 degrees. Make a mark 3 feet along the door and 4 feet along the rail. The rail is at 90 degrees when the distance between the marks is 5 feet. This method works no matter the units -- feet, yards, inches, or anything else. In a right triangle, the square of the longest side is equal to the sum of the squares of the two shorter sides.