How to Paint Trim
The best way to paint trim like a pro is to use an airless sprayer-a sprayer doesn’t leave brush strokes. Sprayers can be rented at many home centers or paint stores. Carefully cover surrounding areas with tape and plastic to avoid overspray problems.
If you don’t want to bother with a sprayer, use a a brush with 100% polyester bristles, such as Purdy’s XL Glide angle sash brush-these soft bristles are less likely to leave brush strokes than are most brushes. Also use a slow-drying paint that “levels out well”-that is, one that is not prone to brush strokes, such as Sherwin Williams ProClassics Acrylic Interior Trim Paint. (Use a latex extender when applying latex paint to trim, as described WHERE TK.)
As with walls, the best strategy for painting trim is to first get sufficient paint onto every part of the trim…and then “lay out” that paint using long, smooth, single-direction strokes. This “lay out” should occur within a couple minutes of applying the paint.