Purchase the best quality primer and paint that you can afford. In the world of paint you get what you pay for. High quality paint will have good "body" (thickness) and excellent flow, which means it will "self-level" to create a smooth surface. Avoid fast drying paints, as these will dry before brush marks can be smoothed or leveled out. If you will be using latex paint, buy only 100 percent acrylic products.
Purchase a high quality paintbrush that will not lose its bristles in your paint. Use the correct paintbrush for the paint you purchased: nylon or polyester brushes for latex paint and natural bristle brushes for oil-based paints. Using a brush with bristles shorter than two inches in length will result in brush marks.
Remove cabinet doors and any movable shelves and lay them flat on a sawhorse or other support. It is easier to paint a horizontal surface, which will lead to a smoother finish.
Remove hardware from the cabinet with a screwdriver, since it is difficult to apply a smooth coat of paint around a hinge or knob and brush marks may result. If you can't remove the hardware, carefully cut in around the knob or hinge and then immediately brush the paint vertically to smooth out any brush marks.
Sand the cabinet surfaces smooth before applying primer or paint using 120- or 180-grit sandpaper. This will eliminate any existing brush marks or other imperfections in the previous paint job. Always remove sanding dust with a damp rag or tack cloth.
Apply primer to porous surfaces that will absorb your paint and dry quickly, since this will lead to brush marks in your paint.
Lightly sand your primer coat with 220-grit sandpaper to ensure a smooth finish on which to apply your topcoats. Always remove any sanding dust with a damp rag or tack cloth.
Apply paint in long, smooth strokes. As you finish a stroke, keep your arm moving and gently lift your brush. Don't overwork the paint or "touch up" spots that are still drying as brush marks will result. Brush strokes are also visible when paint is applied in direct sunlight, to a hot surface or too thinly.
Maintain a "wet edge" when painting by always brushing from a dry, unpainted area back into your wet paint. This will create a smooth, uniform finish to your paint. In order to keep a wet edge, you must apply paint in sections and work quickly. Finish an entire door or drawer surface before moving to the next one.
Start and end your brush strokes where one piece of wood joins another. This will help eliminate brush marks when painting cabinet frames.