If you're using a rattle can, try warming it with warm water before you spray from it. It raises the pressure somewhat but also thins the paint. Then apply two or three thin coats to your model.
Word of caution though. Don't use really hot water (if you can't put your hand into the water, don't use it), don't put the can in the water for more than 5 or 6 minutes max and don't leave it unattended while it's heating.
My buddy who taught me this trick once tried to speed things up. He had a small hot plate and a small cast iron pot that he used to shape styrene with. He decided to speed things up by heating the water to boiling and putting the spray can in the boiling water. Luckily, he shut the hot plate off before putting the can into the water. Unluckily, he left the room for a few minutes. He heard "a pop, a very short hiss and then the sound of something metallic bouncing around". The pressure in the can had risen until it blew the bottom of the can out and launched it like a rocket. Made a hell of a mess (to the room and his models). And in all the years I've known them, don't think I've ever seen his wife as mad as she was that day (lots of muttering about "justifiable homicide" and "idiotic males"). Of course, she was 8 months pregnant at the time and the room was going to be the babys.