I've used MM enamels since they came out in the 1980's, and didn't like them at first back in those days. Now, we've come to terms.
I found that MM's own airbrush thinner wasn't "hot" enough to get a grip on the plastic, and had a lot of trouble with paint pull-ups after masking. For years, then, I used Floquil's Dio-Sol, which was really "hot." Then, Floquil seemed to change the forumla, plus it's gotten kind of pricey--so I switched to lacquer thinner for airbrushing. I sometimes thin as much as 1/2 paint, 1/2 thinner--depending on the color, since some paints seem thicker right from the start, in the bottle, than others.
When I have to brush paint, mineral spirits seem to work fine for thinning. I sort of do it like Tojo says, except I sometimes just use what accumulates in the bottle cap after shaking. Other times I put it on a bottle-cap "pallette," with mineral spirits in another bottle cap. Dip the brush in the mineral spirits, swirl it around in the paint till the consistency seems right, then brush it on.
One thing to be careful of, though, with enamals is not to go back and forth over the area. You will get brush marks.
I think the important thing will be to do some practicing with MM, on some old kits, or some cheap kits that you might not be emotionally attached to very much. Nevertheless, you can get good results with MM.
Good luck.