Components of a typical deck with rails and stairs.(click to enlarge)

1. Use a hammer to refasten protruding nails.
2. Trim raised edges with a sandpaper block, electric sander, or plane.
3. As needed, clean gray or dirty wood with a solution of 1 cup bleach in a gallon of water. Apply with a brush or broom.
4. Use a pressure washer to clean the deck, being careful not to damage the wood with excessive pressure.
5. Apply stain or wood preservative following the manufacturer's instructions.
6. Apply wood sealer following manufacturer's instructions.

Refasten protruding nails.

1. Use a hammer and pry bar to remove the damaged step.
2. Cut new stair treads to fit, using a combination square to cut the ends square.
3. Place the new stair treads on the stringers.
4. Drill pilot holes in the treads where the fasteners will go so that they don't split the treads.
5. Nail or screw the treads to the stringers.

Add support to deck joists:

1. Cut lumber to duplicate the size and length of the existing joist, using a combination square to cut the ends square.
2. Install the new joist against the old one and nail the ends in place.
3. Fasten additional nails, in pairs, every 18 to 24 inches through the joists.
4. Finish the repair by staining or painting to match the deck.

Add bracing to posts:

1. Measure diagonally from post to post and cut the first brace.
2. Set the brace in place and nail the higher end to one end post.
3. Fasten the other end of the brace to the opposite end post.
4. Nail the brace firmly to all posts.
5. If necessary, add a cross-brace between the posts to form an X.
6. Trim off excess wood at the ends.
7. Finish the repair by staining or painting to match the deck.