How to spray car paint depends primarily on 3 things: the car, the tools and the spray paint. They all combine to give you a perfect touch-up at the end of the day.
I will assume you have your tools intact. A Spray gun can give you a better output when you know how to use it. If you intend to spray with custom colors, then you must first mix your various spray paints. For a flat color like black, you only need to get your car ready before spraying.
In any case, start by cleaning your car to remove all the dust particles deposited on the body. Move your car to a wide area where proper ventilation can be experienced. Your spray paint needs air so that it can dry before you spray another.
There are several tips on how to spray car paint that custom painters use that is quite simple and easy to follow. If your car is getting ripped off, use a 300 grit sand paper to remove the spray paints from the body. This is vital and will make the primer to bond effectively. Wipe down the particles with micro fiber cloth after sanding for a clean and smooth surface.
After sand papering the rusty surface, use a masking tape to cover the areas that you do not want the spray paint to touch.
You can now spray the parts with primer lightly. When you light spray the primer, make sure you allow drying in-between between coats. Light spraying primer gradually is better than heavy spray that comes at once.
Wet sand with another 800 grit sand paper after a few light primer coat has been applied. Then wipe again with micro fiber cloth.
Now, this is the final and most delicate step on how to spray car paint effectively. When spraying, go in a smooth and even movement. Do not settle in a spot as the paint would appear heavier there. And again, a few lighter spraying is better than a one time heavy spray. Remember to press and release the button of the spray gun for even results.
You can wet sand again with 800 grit sand paper if you are satisfied with the spray paint output before spraying the clear coat. When spraying the clear coat, spray in the same manner as you have done the spray paint and be careful because this is the layer you are going to be see most. You would not want fingerprints to cause any distortion. Only one or two light coats are needed, allow it to dry.