If you don't like the look of your current wood cabinets or if they're starting to look a little shabby and worn, you should consider refinishing them. Doing so is a great alternative to installing brand new ones and is a much cheaper project to undergo. Just make sure that your cabinets are structurally sound before you proceed. If the wood is rotted or damaged, you're likely to only exacerbate the damage during the refinishing process.
Stripping the Old Finish
First, you'll need to take down all cabinet doors, using the appropriate screwdriver or drill bit. Remove drawers as well. Place the doors and drawers on drop clothes. Wipe down the cabinets, doors, and drawers with a wet cloth, removing any dirt or grime that's built up.
If you're going to be using new hardware (e.g., handles, knobs, and hinges) use wood putty to fill the old holes. If you're going to reuse the hardware, be careful to not fill the holes with primer or wood finish.
Sand the cabinets with fine grit sandpaper, either by hand or using a sander. Excess sawdust will leave behind bumps under the wood finish, so wipe down everything thoroughly with a wet cloth after you've finished sanding.
Refinishing the Cabinets
To re-stain your cabinets, first pick out a stain you like at your local home improvement store. Use rubber gloves to keep the stain off your skin. Brush the stain on evenly, going along with the grain of the wood and cleaning up drips as you go. Then, smooth the stain out and brush away the excess using a clean rag. Allow the stain to dry, and, if necessary, apply a second coat. If you want some extra protection, you can top everything off with a polyurethane finish (or other finish of your choosing).
TIP: If you're looking for a bigger change, you should consider painting your cabinets instead of refinishing them. There are many more color options with painting than with staining.
After allowing everything to dry, you can turn to installing hardware. If you're reinstalling old hardware, simply screw everything back into place, using the same screw holes. New holes will need to be drilled for new hardware, but a power drill makes this job an easy one. Just make sure you measure, so that everything lines up correctly. Then, finish this project by putting the cabinet doors and drawers back into place.