3. Use high quality paint brushes. I am a major cheapskate and I used to buy the cheapest paintbrushes I could. Big mistake. Bristles were constantly shedding onto my projects and they left horrible brush marks. I have since become a huge fan of Purdy paintbrushes. They are a little more expensive up front, but they last much longer so it evens out in the end. And they give a much smoother finish.
2. It really is important to properly prepare your furniture piece first. If you are going for a smooth finish, it is a good idea to lightly sand the entire piece to smooth any flaws. On the other hand, you can probably skip the sanding if you are going for a distressed finish or painting a piece that was in fairly good condition. Regardless of the look you are going with, if your piece has a super shiny or a flaky finish, you should always start by sanding it.