Many people add paint thinner to latex paint to eliminate brush marks on painted surfaces and get a smoother finish. However, paint thinner only waters down the paint without providing any real help in smoothing out the finish. A latex paint conditioning additive such as Floetrol, made by Flood, a wood-stain and paint additive company, is the choice of professional painters. Latex paint conditioner gives latex paint the texture of oil-based paint, binding with the paint to make the paint flow better when applied to the surface. Using an additive, a high-quality brush and quality paint--along with some proper painting techniques--can result in a smoother finish.
Prepare the surface being painted by sanding it with a 100-grit sandpaper. This will make the surface more receptive to the paint and provide a better bond between the paint and the wood.
Mix a small amount of the latex paint conditioner additive with a small amount of latex paint to make sure they are compatible. Additives are made to be compatible with all latex paints. However, any time you are mixing paint with another substance, you should mix it in small amounts to be sure there is no compatibility problem. In extreme hot or cold weather, use more paint additive, up to 16 ounces per gallon of paint. Otherwise, a pint of additive per gallon of paint should be sufficient.
Hold the brush with the handle resting in the area between your thumb and index finger. Use the index finger and middle finger to hold the brush on one side just above the metal band into which the bristles connect. On the other side of the brush use the thumb. Hold the brush in much the same way you would hold chopsticks.
Paint with even strokes, going with the grain of the wood if there is one. Make sure the brush is kept full of paint. Not enough paint on the brush could lead to brush marks on the surface you're painting. Guide the brush over the surface without pressing the brush into the surface. A light touch is one of the best ways of acquiring the desired results.