Check that the rough opening is square, level, and plumb
Remove the prehung door from the packaging
Set the door unit into the rough opening
Center the unit in the opening
Insert shims behind the hinge-side jamb near each hinge
Adjust the jamb until the hinge-side is perfectly plumb
Secure the hinge-side jamb with screws through the shims
Check the strike-side jamb for plumb
Add shims at the strike-side jamb where needed
Adjust the strike-side jamb until it is plumb
Secure the strike-side jamb with screws through the shims
Check the top jamb for level
Shim and adjust the top jamb if needed
Verify the door opens and closes freely
Tighten all fasteners after final alignment
Trim shim ends flush with the jamb
Install casing after the door is plumb and secured