I'd like to add my .02 and recommend a 50/50 mix of mineral spirits & lacquer thinner. I've also had great results with straight lacquer thinner, but it depends on the brand of paint and the temperature & humidity. Best to play around and see what works best. The advice that I always give is to start off with the manufacturer's own recommended thinner; it might be slightly more expensive, but, if something goes wrong, you have some comeback. See here some guide of
How to Thin Enamel Paint for Maximizing Results will help you a lot. Thanks