Measure the rough opening
Check that the opening is plumb, level, and square
Remove the old door and trim if needed
Dry-fit the prehung door in the opening
Place shims at the hinge side
Set the door frame into the opening
Check the hinge side for plumb
Fasten the hinge side through the shims
Check the top of the frame for level
Shim the latch side until the door gap is even
Fasten the latch side through the shims
Check that the door opens and closes properly
Adjust shims if the door binds or rubs
Nail or screw the frame securely in place
Install insulation around the frame if needed
Reinstall or add trim
Install the handle and latch hardware
Test the door latch and swing again