Spray paint is not the ideal product to use on your car. Spray paint is different from automotive paint, and doesn't look the same once it dries. You can use it as a cheap alternative if you don't care about the look of your car, or if you don't want to spend much money on it. The problem you have with a spray-painted hood is that it isn't shiny like the rest of the car. There are some things you can do to get a shine on the hood, though it won't look like a factory paint job.
Place strips of automotive masking tape along the fenders on each side of the hood so that the sandpaper doesn't accidentally scratch them. Place several layers to make the tape thick enough to withstand the sandpaper.
Sand the hood with 1000-grit sandpaper and water. Keep the sandpaper soaking wet while sanding, so that the buildup from the paint doesn't dig into the surface. Hold the sandpaper flat against the surface and sand evenly. Use light pressure against the hood. Heavy pressure can cause the sandpaper to go through the paint.
Move up to 2000-grit sandpaper and sand the hood the same way as you did with the 1000-grit sandpaper, also using water. This lighter grit of sandpaper smooths out the light scratches left by the 1000-grit sandpaper.
Sand the hood one last time, using 3000-grit sandpaper and water to get a smooth, flat finish. Rinse the hood with water and let it dry completely.
Pour a quarter-sized amount of fine polishing compound onto a microfiber towel and polish the hood, by hand. Work the polish in small, circular motions until it creates a thin haze of polish. Let the polish dry for five minutes.
Buff the dried polish away, by hand, with a clean cotton towel. The hood shines as much as possible at this point in the process.
