There are a few methods:
Put down thinner coats of paint, and vary the brushstroke direction between coats.
Don't try to cover the model in one coat, this will also often obliberate small details.
Add a "retarder" to the thinner, prior to thinning the paint. This will slow down the drying time of the paint, produce a more glossy(smooth finish) and also help prevent brushstrokes.
Use high-quality(Artist) brushes, preferably Sable or similar. Hate Nylon brushes myself.
Don't put too much paint onto your brushes.
Guess that is all that I think of the top of my head.