To repaint aluminum siding, apply two coats of primer to the siding, and allow it to dry for at least four hours. Paint the siding starting at the top. Make sure to apply the paint evenly, and don't use too much of it to prevent the paint from dripping. Allow the paint to dry for at least two hours, and then apply another coat of paint to the siding. Make sure to cover all uneven spots with the second coat.
Before you start repainting aluminum siding, make sure to clean it using a pressure washer and special detergents. Sand the siding so that the paint applies evenly. Don't start repainting the siding if it is colder than 50 degrees Fahrenheit outside or if it's raining. Also, don't paint surfaces as the sun shines on them, because it may cause the paint to crack and bubble.
If you can see lines in the paint once it dries, this means that you have painted too slowly and the edges have dried by the time you painted the area next to them. To prevent this, paint small sections at a time, keep the edges wet, and don't pause between strokes. If there are bubbles in the paint when it dries, sand them out. Be careful not to sand the paint off completely, as you might have to repaint the entire surface of the siding.