Dip a dry, lint-free cloth in mineral spirits. Wipe down your composite door's surface with the damp cloth. Reapply the mineral spirits as needed. The use of mineral spirits prepares your composite door for staining by removing dirt and dust.
Apply painter's tape around the doorknob and hinges. If your composite front door has a window or peep hole, tape that as well.
Lay a dropcloth down in front of the door. This protects your porch or stoop from a spill.
Open the container of stain. Mix it well with a paint mixer.
Dip the natural-bristle paintbrush in the stain. Wipe excess stain off the paintbrush by scraping each side of the brush against the edge of the can.
Apply a thin coat of stain to one side of the door, using even, vertical strokes. Let the stain dry. Prepare and stain the other side of your composite front door in the same manner.
Paint your freshly stained composite door with a thin coat of protective polyurethane. Apply the protective finish with a 2-inch-wide foam brush. The polyurethane finish dries over the stain, helping it retain its color.