Allow the new coat of oil-based paint to dry completely.
Sand lightly over the oil-based paint to apply a "tooth" to the surface, which helps new paint adhere. If the paint is very thick, bubbling or peeling, use an orbital sander to completely remove it from the surface.
Wipe down the area with a damp cloth where you've sanded, to remove dust and other residue.
Apply an oil-based primer over the original paint job in white or a color that matches your final color. Allow the primer to dry overnight. Using an oil-based primer will ensure that there is proper adhesion between the paint you want to cover and the new paint you want to apply. The primer's job is to form a bond between the layers of paint.
Paint a coat of the new color on top of the primer. It doesn't matter if your new paint is water- or oil-based if you use a high quality, oil-based primer. If you use a tinted primer the same color as your final paint, it will save you at least one coat of paint. Allow each layer of paint to dry fully before applying another coat on top. This helps prevent bubbles or wrinkles from forming in the paint.
Add a second or third coat of the new paint, if needed, to complete the new paint job.