Put on latex or rubber gloves. Mix one-quarter cup TSP with one gallon warm water in a bucket. Position a ladder safely in front of one of the dormer windows. Climb the ladder carefully with the bucket in hand.
Dip a sponge in the mixture and wipe down the exterior of the dormer windows, including all areas that you plan to paint. Rinse with a garden hose. Allow the exterior dormers to dry thoroughly.
Sand the exterior of the dormers with 180-grit sandpaper. Rub the sandpaper against every area that you plan to paint. Run a soft cloth across the exterior dormers when finished.
Tape off all areas that you don't want to paint---particularly the glass around the panes of the dormer windows---with painter's tape. Dip a trim brush in latex primer and apply an even coat to all exterior features. Allow it to dry for at least an hour and apply a second coat.
Dip a three-inch nylon paintbrush into latex paint and apply a base color to all the designated areas. Allow it to dry and apply second coat.
Rinse off your paintbrush and apply a second color of latex paint to the trim of the dormer windows. Remove painter's tape from the exterior before the paint dries.