Brushing is an Art all by itself, and requires lots of practice to get good results… most importantly use a FLAT EDGE brush, NOT the popular Angle Edge ones, which beginers think are easier for them… just the opposite, and the Quality of your topcoat Brand will also make a difference, use a good High Quality Brand like Sherwin Williams or Behr… Also Using Paint with Primer is NOT advised… it is a “Gimmick” that manufacturers use to sell more paint, and may make Brushing for beginners more difficult… besides you already Primed the surface! Good Luck!