Knowing both the fine print and your rights as a passenger will help. Be ready and be flexible if traveling on a free ticket. If you are a full-fare passenger, know what priority you are and speak to the gate agent if you think a mistake is being made. Don't assert rights that you think you have but don't, the agents will peg you as uninformed and treat you as such. Ask nicely to speak to a supervisor. Take down the name of the person you are dealing with. Never raise your voice or threaten, you will immediately take yourself out of any consideration and place yourself in a security risk position. Follow all the rules. And yes, I've been bumped more times than most people have flown.
Mandi