Painting your oak furniture may hide its attractive grain, but sometimes that's the best way to deal with gouges and nicks that would show up under a clear finish. The most important part of the process is "prep," which is a painter's term that refers to preparing or stripping the old finish, sanding and filling the nicks and gouges. If the furniture has any loose joints or lifting veneer, make needed repairs as part of the prep to ensure a seamless painted finish. You get the best paint results by spraying, but a well-executed brushed finish also looks attractive.
Clean the old finish -- if it's in good shape -- by washing it with a solution consisting of 1/2 cup of trisodium phosphate detergent per gallon of water. If the finish is cracked or peeling, with a methylene chloride stripper. Use a soy- or citrus-based stripper as an alternative; it will work more slowly, but it's safer for you and the environment. Clean the stripper residue with TSP and water, rinse with clear water and let the wood dry.
Sand the stripper residue with 120-grit sandpaper. A palm sander speeds up this job when you're working on a piece of furniture with a number of large, flat surfaces, such as a cabinet. If you're painting an item with many turnings and carvings, such as a chair, it's safer to sand by hand.
Make all structural repairs, such as gluing joints or replacing lifting veneer. Glue with PVA adhesive or carpenter's glue. Clamp anything you glue overnight using bar clamps or C-clamps.
Fill nicks and gouges with epoxy wood filler. Since you're painting, you don't have to worry about color matching, and epoxy filler makes a more permanent repair than latex- or solvent-based wood fillers. Mold any repairs that you make with a putty knife while the filler is stiff, but hasn't set yet.
Sand once more -- by hand -- with 150-grit sandpaper. If you didn't strip the finish, this is the sanding you need to do prior to applying finish. Be sure to sand all the filler flat.
Apply a single coat of high-solids wood primer. This is a necessary step whether you stripped the old finish or not -- paint adheres better to primer than it does to wood or wood finishes. Spray the primer from a can or apply it with a paintbrush.
Scuff the primer lightly with 220-grit sandpaper and apply a coat of the paint of your choice. Oil-based and latex enamel are the most reliable paints for wood furniture. Spray either from a can or with an air spray gun, or brush it. Use a natural-bristle brush for oil-based paints and a synthetic-bristle one for latex paints.
Let the paint dry overnight, then scuff it lightly with 220-grit sandpaper and apply another coat. You shouldn't need any more than two coats, but if you do, let the second coat dry, sand and apply a third coat.