Acrylic car paint comes in two forms: acrylic enamel paint and acrylic lacquer. The two are totally non-compatible and should not be used together on the same paint project.
1. Using Acrylic Paint
Acrylic enamel paint is simple to use and pliable to work with. Acrylic lacquer paint takes multiple applications, so you would need more than two coats. If you find any blemishes in the paint they can be easily removed.
Acrylic lacquer also dries quickly, which means that any imperfections you find can be dealt with more rapidly. If you use a spray gun, hold it about 10 to 12 inches from the car when you paint.
Prepare the surface of the car correctly and you could safely spray acrylic enamel over the top of acrylic lacquer, but using them the other way around is strongly advised against. Always prepare the surface of the car body properly.
3. The Previous Coat
Always check the type of paint that is on your car before you decide to paint over it. If the paint you have on already is incompatible with the acrylic you use, then you will not only find more blemishes that cannot be easily removed, but you may also find that the paint comes off after a very short time.