Choose the Right Paintbrush
Paint can hide many imperfections, but if it's not applied properly, it can reveal them as well. If you aren't careful, you could end up with bubbles or bristles on the wall.
One of the most important tools for painting is the paintbrush. When purchasing one, make sure that it has flagged bristles, which help the brush hold more paint and spread it more evenly. The bristles should also be "chiseled," with the middle bristles longer than the outer ones. For trim work, use an angled sash brush.