Measure the rough opening
Remove the old door and frame if needed
Check the opening for level, plumb, and square
Repair any damaged framing
Apply flashing tape or waterproof membrane to the sill and opening
Dry-fit the new exterior door
Place the door in the opening
Shim the hinge side until the frame is plumb
Secure the hinge side with screws through the jamb
Check the door for proper swing and even gaps
Shim and fasten the latch side
Shim and fasten the top jamb
Install additional screws through the jamb as needed
Insulate gaps around the frame with low-expansion foam or backer rod and sealant
Install interior and exterior trim
Caulk around the exterior trim
Install the threshold and weatherstripping if not already attached
Test the lock, latch, and door operation
Paint or finish the door if needed