Preventing unsightly brush marks is a simple matter of using the right paint, buying a good brush, going with the grain and letting gravity give you a little help.
Buy a paint brush that is of good quality. Bristles on these brushes have varying lengths, longer in the middle than on the sides. Also, the bristles should have split ends, which hold onto the paint and allow for a smoother application.
Buy paint labelled slow-drying. The 24-hour drying time gives the paint time to spread out on its own, thereby reducing brush marks.
Whenever possible, paint on a horizontal surface. Gravity helps prevent brush marks. Take down doors before painting. Paint door trim on a flat surface before installing.
Paint in the same direction as the wood grain and strokes will not be as noticeable.
Let dry thoroughly after first coat, then apply a second one.