Apply Duplicolor Touch-Up Paint by prepping the area, applying the color coat, applying the clear coat, and then polishing with rubbing compound. Like any other paint process, the key to a good touch-up job is patience, cleanliness, and through surface preparation.
The most important step in painting is cleanliness. Any foreign material keeps the paint from adhering, so ensure the area is completely clean and dry before each step of the process. Spray the floor with water to keep dust from rising up while you're working. If possible, only paint when it's at least 50°Fahrenheit for brush cap bottles and paint pens, and at least 70° for car spray paint.
All cars have at least three layers of paint: the primer, the color coat and the clear coat. The depth and shape of the damage determines the proper surface preparation technique. If there is rust or bare metal, then all three layers have been penetrated. Use 220-grit sandpaper and/or rust remover to remove the rust, then apply a thin coat of primer and let it dry overnight. Feather the edges of wide scratches with a sanding pen, making a "U" shape, so the transition between the original paint and the touch-up is smoother.
Apply only the minimum amount of paint needed to cover the primer. For very small areas, dip a toothpick in the paint, touch it to the area, and let capillary action pull the paint onto the surface. Let the paint dry overnight, and then apply several thin coats of clear coat. Let the clear coat dry for three days, and polish with rubbing compound to blend your repair with the rest of the finish.