Be ready to talk in depth about your research. You should be able to have a conversation about your work and results. Practice explaining your research to your parents, friends, teachers, especially people who don't understand your research. Tell everyone to ask you at least three questions.
Judging rubrics are available at rubrics. These rubrics less the scores will be provided to the students after PRSEF.
Judges look for well thought-out research. They consider how significant your project is in its field, as well as how thorough you were in conducting your research. Did you leave something out? Did you start with four experiments and finish only three?
Judges recognize students who can speak freely and confidently about their work. They are not interested in memorized speeches but prefer simply to TALK with you about your project to see if you have a good grasp of your research from start to finish. Note cards are permitted, but students should not read from them. Besides asking the obvious questions, judges often ask questions to test your insight into your project, such as, "What was your role?" or "What didn't you do?" and "What would be your next step?"
Judges expect you to demonstrate that YOU did the work.