Sachman - here's the link to Don's website: sites.google.com/.../donsairbrushtips
It is quite invaluable to anyone wanting to learn the basics of airbrushing.
I see he also has an online book now.
I'll echo Phil - thinning is a personal preference. I use mainly acrylics. When I started out, I thinned around 2:1 paint to thinner, as this was what most people seemed to suggest. I also used to use around 15-20 PSI.
However, after my own experimentation, I now prefer a 50/50 mix at around 30 PSI. It means you take longer to build up coverage and may be more prone to runs etc when first learning (due to thin paint and high pressure), but it's what I prefer. Also, given it's acrylic, the higher pressure evaporates the alcohol base very quickly, so it touch tries almost instantly (though should always be properly cured before masking etc).