Not too long ago, I discovered one of the tricks to getting a decent seat on Southwest Airlines. I printed out my boarding pass before leaving for the airport. As a result, I ended up in the first boarding group and had my pick of the best seats. I didn't arrive at the airport hours in advance either. Another great way to find the best seats in coach is by calling the airline before departure. Some of the seats saved for preferred customers are freed up 48 to 24 hours ahead of time.
Where you sit is important, too. You can find out more about where the primo seats are by using a Web site called seatguru.com. They list which seats on specific planes have the most legroom, which ones don't recline, which ones are near emergency exits, and even where you might have a difficult time seeing the on-board movie!