Steven,
Up until I bought my Iwata recently, I used the same airbrush as you for over two years and I found it was a matter of well thinned paint, lower the pressure and keep the airbrush very close to the model. You then need good control on the button, I wouls suggest using the adjuster nut in the cut out to tighten the mechanism so that you have more control over the paint and airflow and concentrate, do small areas at a time and take breaks and rest your eyes and fingers.
I found the best way was to practice, practice, practice on some paper or a similar scrap surface and figure out the best ratios of paint to thinner to air, to distance and it will work very well.
It is easy to get put off if you initially dont get the results you want.
I hope this helps,
John