Scrub the splintered, chipped or dented area with a stiff wire brush to remove any loose paint or wood chips.
Apply a waterproof glue to any splintered pieces and clamp them until the glue dries.
With a putty knife, spread a paste wood filler over the damaged area, covering it completely.
Smooth down the wood filler until it is flush with the wood surface. Let dry overnight.
Sand the patch gently with 220-grit sandpaper, feathering out the edges to make the patch less visible.
Wipe off the sanding residue with a damp cloth.
Remove any peeling paint with a stiff wire brush.
Sand the item with 120-grit sandpaper, along the grain.
Switch to 180-grit paper, and sand again until the item is fairly smooth, especially along the edges between the painted and unpainted areas.
Paint any bare wood with a primer; let dry.
If the wood has a number of knotholes or dark blemishes that you want hidden, paint them with a stain-killing primer. Let dry.
Paint the entire piece with an exterior paint--even the hard-to-see places underneath, which will need the paint for protection, if not appearance. Let dry.
Apply a second coat; let dry.