This really isn't paint, but Future is applied with a brush and/or airbrush. Following is how I do it:
Future Prep: I use 2 ounce bottle and mix Future with Windex in a 75/25 ratio. I have found this allows my airbrush to atomize the Future better. It also seems to brush smoother as it is not as thick.
Brushing: I use a very clean brush. For large surfaces, like aircraft wings, I use a broad sable haired brush. For smaller areas I use a #2 small flat brush. I usually brush two thin coats, waiting 10-15 minutes between coats. As future is self-leveling you don't have to worry about brush marks. If you do make a mistake a small amount of Windex on a Q-Tip cleans it right up.
Airbrushing: I generally sprays two medium heavy coats, waiting 10-15 minutes between coats. Before I started thinning my Future I sprayed several thin coats to avoid any runs, but I found this frequently left a "grainy" feel to the surface. Since I started thinning I have not had any problems with runs, just keep the airbrush moving; the same as with paint. If you do get a run, it can be cleaned up using the same technique as above. Also, if you end up with that "grainy" problem above, you can spray a light "flash coat" of Windex and it will smooth it out.
I always wait 24 hours before applying decals ro let the Future cure.
Ernest