Remove the old door, trim, and casing
Measure the rough opening
Check that the opening is plumb, level, and square
Shim the rough opening as needed
Place the prehung door into the opening
Center the door in the opening
Check the hinge side for plumb
Insert shims behind the hinge locations
Secure the hinge side with screws through the jamb and shims
Check the latch side for even reveal
Shim the latch side as needed
Secure the latch side with screws through the jamb and shims
Check the top jamb for level
Add shims and fasten the top if needed
Test the door for smooth opening and closing
Adjust shims if the door binds or rubs
Trim excess shim material
Install casing around the door
Fill nail holes and gaps as needed
Paint or finish the trim if desired