Staining a chair is a simple operation; in most cases you brush or wipe on the stain, and it penetrates to provide an even hue. For this to happen, however, the wood must be properly prepared, and that usually involves a fair amount of effort. You have to remove all the existing finish and stain, and that usually involves caustic strippers. Then you need to sand, and if the chair has turned legs or other ornate features, getting into all the nooks and crevices can be painstaking. A rotary tool may make the job a little easier.
Find a well-ventilated place in which you can work and leave the chair overnight to dry. Cover the floor with newspaper.
Strip the finish, if there is one, with furniture finish stripper. It is not as strong as some paint strippers, but you still need to wear protective clothing, rubber gloves and a mask.
Paint the stripper onto a section of the chair with a paintbrush and wait for the finish to start bubbling. While the stripper is still wet, scrape off what you can with a putty knife and scrub off the rest with fine steel wool. Keep the steel wool clean by dipping it in lacquer thinner. Because lacquer thinner is a strong solvent, it will help remove the finish.
Take the chair outside and wash it off by spraying it with a garden hose. This washes off residue and, more importantly, neutralizes the stripper. Let the chair dry for several hours before proceeding
Sand large flat areas of the chair with a pad sander and 100-grit sandpaper. Fold the paper over and use it to sand curves and round areas by hand. Sand in the direction of the wood grain.
Use a rotary tool with a grinding or sanding accessory to sand in crevices you can't reach with folded sandpaper. Run the machine at low speed to avoid wearing down the wood and changing its shape.
Switch to 120-grit sandpaper and sand again. By now, most of the old stain should be gone. You may have to settle for dark bands around some of the more difficult-to-sand areas. These dark bands help give the chair an antique appearance. Finish the sanding job by going over the piece once more with 150-grit sandpaper.
Wipe the chair with a damp rag to remove all the sanding dust. Stir a can of stain with a wooden stir stick until all the solids are thoroughly mixed, then paint it onto the chair, starting at the top and working toward the bottom. Work in 10-minute segments, going back after completing each segment and wiping what you've done with a clean rag.
Apply gel stain with a rag as an alternative to brushing on a liquid stain. Gel stain won't run and covers evenly, but you have to be more rigorous about wiping off the excess.
Leave the chair undisturbed overnight to allow the stain to dry.