Remove the door from the hinges
Inspect the frame for cracks, splits, rot, or loose joints
Tighten or replace loose screws in the hinges and strike plate
Remove damaged trim or molding
Cut away rotted or broken wood
Fill small cracks and holes with wood filler or epoxy
Replace severely damaged sections of the frame
Cut a new piece of lumber to match the damaged area
Apply wood glue to repair joints
Clamp repaired sections until fully set
Sand repaired areas smooth
Reinstall or replace the strike plate
Rehang the door and check alignment
Shim the frame if needed
Repaint or refinish the repaired area