airbrush paint spray problems

The paint should be thinned to the consistancy of thin (2 percent) milk as a rule of thumb.

Polyscale acrylics, for example, require little thinning, whereast Tamiya requires substantial thinning.

Generally, it is best not to thin for hand brushing. Again using Tamiya as an example, in warm or dry weather, dipping  your brush in a drop of isopropyl (90%) occasionally will keep the paint fluid on your brush.

What pressure are you using? Sounds like you could be using too low a pressure or too high a paint volume.

There's an article available from a pinned thread, here, called "The ABCs of Airbrushing." Download, read, and save for reference—its a great resource!

Most of this is a matter of experimentation—find what works best for you—but don't hesitate to ask questions.