To add some "age" to the piece, apply black spray-paint sparingly and sporadically over the surfaces to emulate aging and water damage. Apply more black paint toward the bottom areas of the piece, creating an effect that would be expected from a piece that had been exposed to water or had sat on a dirt floor.
Note: This technique is not recommended for authentic antiques, but can be used to good effect on unfinished furniture, which can be purchased fairly inexpensively from stores specializing in unpainted and unfinished furniture.
Decide on a color for your piece. Typically, country furniture was painted using left over paints from other projects.
Paint the piece using an ordinary paintbrush. Start brushing paint on at the top of the piece and proceed downward so that, there is less paint on the brush when the bottom has been reached. Avoid covering every inch of the surface to create the illusion of some wear and tear.
Once the paint has been applied, wipe it with a rag before the paint has dried. This results in a more muted, antique-looking finish. Take your time and use your imagination to give the finished piece a look that imitates the effect of aging and wear.
Finally, you may want to apply some extra protection using a water-based spray-finish. Use a satin finish rather than a high-gloss. A shiny high-gloss finish would not be in keeping for a naturally aged piece. A satin or matte finished is much better suited to the mellowed, antique look.