 There are several different kinds of primers on the market. Some are designed to cover and block stains, others are good for hiding existing colors and patterns, and some just do it all. Your local paint store or home center can tip primers, and I recommend this when using darker paint. Most jobs only need one coat of primer, but consider applying two over very dark colors or bold prints. Now, once the primer is dry and you begin applying your chosen color, you're going to notice that you can spread the paint smoothly and evenly. Smooth and even are good things when it comes to painting.