You are getting bubbles because you are spraying too heavily, moving the can too slowly across the surface, spraying from too close a distance or any combination of the three. There is too much paint getting to the surface, it's pooling and dissolved propellant in the paint is outgassing, forming bubbles. The surface of the paint is skinning and the bubbles have no way to escape.
Unfortunately, the only way to remove the air bubbles you have in your paint finish is to sand out the bubbles and re-paint.
Before spraying, warm the can by standing it in a basin of warm (not hot) water. Shake well - at least 3 minutes.
When you use a spray can, you should not be any closer than about 10-12 inches from the surface being sprayed.
Move the can parallel to the surface - maintain the same distance for each pass of the can. Do not cover the area by twisting your wrist - swing your enitre forearm from your elbow using a smooth, even, continouos motion. Begin the spray before you reach the subject and continue past before releasing the button (this prevents "spatters" of paint landing on your model).
Spray cans deliver a lot of paint very quickly, but don't try to cover in a single coat. Apply multiple thin coats rather than a single heavy coat. Start with a light "mist" coat, allow to dry (about an hour or so) and repeat. Repeat this process again before applying a "wet" coat.