It is important to thoroughly shake the can prior to use, and occasionally during use as well. The can should be shaken for no less than one minute after the mixing ball in the can begins to rattle. This ensures that the product is mixed well, and prevents larger particles from being sprayed through the nozzle.
Also, make sure the finger that presses down on the nozzle stays clean and free of any paint. It is important to have your index finger centered on the nozzle itself. If your finger is too forward it can cause some blocking of the spray mist as it comes out of the can, which can cause sputtering or larger drops to be sprayed on the surface.