Home Improvement : Painting Exteriors: Prepare the Surface First : Some things to consider about before you take your brush in hand.

A good exterior paint job can greatly improve your home’s appearance and add to its value.

But before you take brush in hand, all surfaces that will be painted must be made ready. Dirty or flaky surfaces will not hold paint for long.

Remember that loose boards, leaky gutters and faulty caulking will undermine the best paint job.

CONCRETE: Scrub oily, greasy spots with hot water and a detergent such as trisodium phosphate. Rinse thoroughly and allow to dry. Patch all holes and cracks. If the surface is scaly or flaky, brush vigorously with a wire brush. Finish by vacuuming the entire surface.

WOOD SIDING: Examine all areas of the structure being painted. Make sure it is free of defects, particularly those that permit water to penetrate the wood behind the paint and cause peeling and blistering.

Here are some trouble spots you should correct:

--Clogged outlets and downspouts are another source of trouble. Clean them and keep them free of debris at all times.

--Repair or replace drip cap flashing at the tops of doors and windows.

--Check door and window joints for cracked or loose caulking. Remove loose material and recaulk.

--Check windows for crumbling or missing putty and replace it if necessary.

--Check for loose boards. Nail them in place, then sink the nails and fill the holes with wood putty to prevent rust stains.

--Patch damaged boards or replace them. Seal exposed knots in siding with shellac to prevent discoloration by the resin in the knots.

--Clean metal casement windows and railings thoroughly. They should be free of dirt, rust and grease. Use a wire brush to remove loose rust and peeling paint, then sand to the bare metal. Follow with a coat of metal primer.

--Remove blistering, peeling paint with a wire brush or scraper. Large stubborn areas may require a chemical paint remover or electric paint softener. Paste-type chemical removers that cling to vertical surfaces are best. Be sure to wear protective gloves and do a small area at a time.

If damage is extensive, remove the paint down to the bare wood, then sand the edges of the remaining paint smooth. Prime all bare wood with a color compatible with the final topcoat.

WOOD SHINGLES: Check for loose or warped pieces and renail them with aluminum nails. If the building paper underneath appears damaged or torn, slip a piece of roofing paper the size of the shingle under the shingle before nailing it down.

Need help on a home repair or improvement project? Write Reader’s Digest, P.O. Box 700, Pleasantville, N.Y. 10570-7000. Suggestions and tips will be offered in future columns.