To install a door and frame, prepare the wall framing for the casing frame, mount the frame casing, fill the gaps between the frame casing and the wall framing, and attach the door onto the casing. Testing the door by closing and opening it completes this process.
To prepare the wall framing for the casing frame, first inspect the door frame to ascertain if plumbing and leveling is necessary. Drop a plumb line from the frame's top on one sides of the framing to plumb if needed. Locate out-of-plumb points on the framing, determine the framing adjustment measurements by measuring the casing frame, and use shims to plumb the points appropriately.
Once the framing is plumb and level, insert the frame casing into the framing, readjust the framing as needed, and secure the casing into place with finish nails, taking care to ensure that the nails attach the casing at the shims. Using shims, fill any gaps between the framing and casing as needed. Attach the door onto the casing with hinges, and secure it in place with hinge screws. To prevent door sagging, remove and replace one of the hinge screws from the top hinge with a screw that is long enough to run through the frame casing into the framing wall.