From DIYinfo.org
When you have stripped any old finish, it will be necessary to prepare the bare wood for refinishing. If possible, preserve the patina of the old wood by doing nothing more than lightly sanding raised grain. You will also need to prepare and finish any new components that you have substituted for damaged or missing parts. Do not be fooled into thinking that a wood dye or a layer of varnish will disguise a poorly prepared surface - in fact, a clear finish tends to draw attention to raised grain, scratches and dents. It is important to repair the worst blemishes before sanding the surface with progressively finer grades of abrasive paper.
[edit] Pieces to be Painted
If stripped of its old finish, a piece to be painted does not require the fine sanding so necessary to those pieces that will receive a clear coating. However, the surface must be smooth. Following the repair work and the patching, sand the surfaces with medium grade cabinet paper until you achieve an un-pitted, even surface that will take the paint coating smoothly.
The scratches from paper coarser than medium grade will show through most paint coatings. If you are going to paint over an old finish, after repairing the piece and cleaning it of any wax or grease or dirt, then you should sand it with medium grades just as you do the raw wood pieces, paying attention to feathering out (smoothing) the edges of any chipped or flaking paint areas.
[edit] Filling in Blemishes
The fillings used to fill small holes are made in a range of typical wood colours. However, as they do not absorb dyes and finishes quite like the surrounding wood, some restorers prefer to sand the wood first and apply one sealer coat of finish before trying to match the colour of the filler. Others prefer to fill first, having already tested a sample on another similar piece of wood or on an inconspicuous piece of the furniture, and having applied the requisite finish to see how it reacts with the filler.
[edit] Stopper
Stopper is a ready mixed paste with a consistency similar to putty. It is possible the best filler to be used with paint, although it can be used under most finishes. When using a clear finish, choose a stopper that is close to the colour of the wood, then adjust a small batch by adding a compatible wood dye until you achieve the exact match. A less-than-perfect match can later be disguised with very light application of artist's oils colours. Ensure the surface is clean and dry, then use filling knife to push stopper into the crack or hole. When it has set firmly sand lightly until flush with the wood.
[edit] Filling With Wax
Coloured wax filling sticks are ideal for woodwork holes and hair line cracks before applying wax polish or shellac. Cut up small pieces of wax and need it between your fingers until it is soft enough to push into the holes with a blade. As the wax hardens scrape flush with a piece of flexible plastic and then burnish the repair with the back of a piece of sand paper.
[edit] Melting solid shellac sticks
Using a soldering iron to melt some solidified shellac into a hole and, while it is still soft, press it flat with a chisel dipped in water. Once the shellac has hardened, pare it flush with the wood using a sharp chisel, before sanding it smooth with a fine abrasive paper.
[edit] Removing Scratches and Burns
A burn left by a carelessly placed cigarette or a scratch across the grain can often be sanded out with abrasive paper. However, it is quicker to remove deeper blemishes with a cabinet scraper. As scraping is almost certainly going to cut below the level of the patina, you may have to blend in the small scraped patch with wood dye.
[edit] Tip for using a scraper
Always scrape diagonally across the grain of the wood from opposing directions, then finish by scraping parallel with the grain.
[edit] Raising Dents
[edit] Applying Water
Use a pointed paint brush to drop hot water on to the dent, then allow the wood to absorb the moisture. Once the wood appears to be dry apply more water until the dent disappears. Should this treatment prove unsuccessful, try using steam.
[edit] Using steam
Lay a damp cloth over the dent and place the tip of a soldering iron directly on top. The steam generated should cause the grain to swell. Once the surface is flush, sand the whole area smooth with fine abrasive paper.
