1. Slow down. You've run the same piece over and over in your bedroom, and it's clocking in around 3 minutes. When you get in front of a crowd of people, though, you somehow clock in around 2 minutes and 30 seconds. Know that when on stage, most people tend to rush. Really pay attention to those pauses, which often get rushed through when nerves kick in. Timing is incredibly important in slam. You have to give your audience some time to digest what you say. If you speed through and don't give your poems/stories room to breathe, the best parts get lost in the shuffle.
2. Watch those feet! I have a bad habit of shuffling on stage and sometimes swaying side to side. Because of that, I'm sure people have been distracted by my "little dance numbers" that have taken place when I'm trying to perform a serious poem. Plant your feet firmly, but don't lock your legs.
4. Videotape yourself or have a friend do it. This is the best teacher you can have. You may find yourself saying, "Holy shit! I sound like I'm running a relay race with my mouth!" or "Why are my hips gyrating during this really sad part?" Many people idealize their performances. A reality check in the form of watching yourself is a brutally honest tool that pushes you harder to achieve the performances you want to give.
5. Remember why you wrote the piece in the first place. Take a moment before you step up to the mic and remind yourself what you wanted to accomplish with the piece you are about to perform. I do this every time I get on stage, because it amps up the passion of my performance. Mean what you say. If you are performing a piece about a social justice issue you want people to know about, don't just say memorized words at an audience. Bring the same fire you would when you are talking about it with friends. Bring the same fire that drove you to write the piece to begin with.
6. Humble pie is part of a balanced diet. You're going to mess up on stage. It's inevitable. You won't always make it to the final round. It happens. Not only should you accept that it happens, you should know that it's okay. I would be not be the performer I am now if I didn't mess up every now and then. There have been times I've been sorely disappointed on stage with either my performance or the outcome, and I've felt like a giant failure. But I'm not. In fact, if I didn't have those experiences, I wouldn't push myself as hard as I do to improve.
7. Always push yourself. There is always something you can do to improve. There are new styles and new forms of poetry and storytelling, and you should learn them. Try new things. The people who come out on top didn't get there by merely being satisfied with themselves. Think about where you would like to go with your writing. Like the Reading Rainbow says, "We can go anywhere," but it sure as hell won't happen if you don't push yourself.