Step one -

Protect your eyes and skin by wearing safety glasses and disposable rubber gloves. Remember, anything that can permanently stain wood will stain fingers, too. Also wear old clothes to work, since some stain could spill.

Step two -

Always test stain on a piece of scrap wood before starting on the furniture.

Step three -

So that the stain doesn’t leave blotches on the wood, always apply a thin coat of wood conditioner first by brush (gives a smooth finish for the stain to work on). Give the conditioner about 15 minutes to dry before applying the stain.

Step four -

Oil-based stains, which are the most common, consist of dyes and pigments mixed in with mineral spirits. Make sure to stir the can thoroughly before staining to bring the dyes and pigments up off of the bottom. When working with oil-based stains, there will be fumes, so make sure to always work in a well-ventilated area.
To avoid fumes, go with a water-based stain. One of the advantages to water-based stains is that they come in a wide variety of colours, even more colours than the oil-based. Apply the water-based stain in the same way as oil-based.

Step five -

 Apply stain with a brush or a rag, depending on preference. With a brush, work both with the grain and against it. Don't worry about being neat; all that matters is getting a nice, even, liberal coat over the wood. At this point, wipe the stain off immediately for a lighter tone, or for a deeper tone, leave it on for five or even 10 minutes before wiping.
Be sure to wipe off all the excess stain going in the direction of the grain of the wood. That will guarantee that the stain gets into the wood, instead of laying on top -- and it really shows off the grain of the wood to advantage.
If the stain needs to be darker, go back over and apply more stain.

Step six -

Stain only provides colour, not a finish. Always apply a finish on top of stained wood. Or, if time is short, reach for a product that combines both stain and finish with one coat. The product will need to be brushed on more carefully, finishing by brushing with the grain of the wood. Use a higher-quality brush with this type of stain/finish.