Put a drop cloth under the bare wood window and remove any treatments such as drapes or blinds.
Gently brush over the bare wood with steel wool, removing any dirt and dust.
Abrade the bare wood with medium-grit sandpaper. The goal is to smooth any rough spots and rid the bare wood of any splinters. Wipe the wood with a tack cloth to remove any dust once it is well sanded.
Adhere painter's tape between the bare wood and glass panes. This will keep you from accidentally getting paint on the glass as you paint the bare wood window. In addition, stick painter's tape around the outer edges of the wood window so as not to get paint on the wall.
Apply a coat of primer to the bare wood window, brushing it on with the direction of the wood grain, as much as possible using a paintbrush. Let the primer dry for two to three hours.
Apply the first coat of oil-based paint to the primed wood window, following the wood grain with a paintbrush. Let it dry for three hours. Apply a second coat of oil-based paint and let it dry to finish.