As I always make a mess of the (hand)paint job

, I thought I’d try my hand at airbrushing. I bought a Revell Alpha airbrush. It works fine with Tamiya Acrylics, but I have a problem in getting a constant cover. I realize this will take practice, but it (the paint) is either to thick or to thin (watery). What ever the thickness, I end up spraying the model to long and I get runs, or a build up of paint in certain areas which covers all detail.
So here’s my question.
I read a lot about people saying when they airbrush, I use 70% thinner and 30% paint. How do you get them into a container in those ratios, or any other ratio for that matter ?? What is a good paint/thinner ratio ?? What do you use for thinner (in Holland) ?? I’ve tried Tamiya Acrylic thinner, but it’s a bit pricy.
Any tips would be greatly appreciated