Examine the hinge screws to see if they have pulled away from the frame. If so, remove the hinge screws and replace with screws of the same or slightly larger diameter and at least 1 inch longer that will fit through the hinge mounting holes.
Check the gap between the top of the door and the frame. If it is not uniform all the way across, loosen one set of hinge screws two turns of a screwdriver and tighten the other set of screws two turns of a screwdriver. Tighten the top hinge if the door is tilting down and the bottom hinge if the door is tilting up.
Remove the strike plate screws and the strike plate. Reposition and mark the new location of the plate. Chisel the perimeter to size and drill into the frame 3/4 of an inch with a drill bit the size of the lock bolt. Replace the strike plate.