How to make paint last longer on your brush

Depending on the circumstance I use a variety of mediums. At times it appears that I can paint quite a few strokes before needing to reload, while other times I reload after only 2-4 strokes. I typically aim for very thin, similar to being airbrushed on, smooth surface paint reserving any paint “standing proud” for the last highlights. I thin my paint so that it flows on the panel easily.