Measure the width of the door frame on your soleplate and mark the width; this is the rough opening for your door. Mark the soleplate every 16 inches on each side of the door marks.
Cut two 2-by-4 studs to 80 3/4-inches and toenail (drive a nail at a 45 degree angle through the stud and soleplate) them to the soleplate. These studs are known as triggers.
Nail standard length 2-by-4s (king studs) to each trigger, outside the rough opening.
Cut a 2-by-12-inch header 5 inches wider than the door frame and place it atop the triggers and between the king studs. Nail it into place by nailing through the king studs.
Toenail a 2-by-4 stud to the soleplate at 16-inch intervals.
Lay another 2-by-4 (top plate) along the other end of the studs and toenail it to the studs. Lay an additional 2-by-4 (doubler) on the top plate.
Cut the soleplate from the rough opening, insert the door frame and nail it to the triggers with finish nails from inside the frame.