I like to use a red blue and filters then do a wash of black.
My filters are like 95%thinner ( alcohol,water or a spirit type ) and 5% paint and if I use water for my thinner then a drop of dishdetergeant.
Then for my wash I like to mix it a bit thicker for the paint, anywhere from 80% to 90% thinners ( same as the filters for the thinners ) then the rest would be paint.
Either way the liquid mixture is really thin and watery so it goes on really easy, after all that is dried for at least a day then it's time for the pastels.
I almost forgot I also use a brush to apply my goodies, but I now have a crappy single action airgun to use so I guess I'll be trying it out for my small applications.