Most dissertation candidates will likely know a few members of their committee, but even if you have never met your committee members, make an effort to research their backgrounds. Pay particular attention to each person's professional experience, published works and research specialty. Familiarizing yourself with this information will help you anticipate some likely questions and comments that you might encounter during your presentation as well as help you to target your presentation to your committee's preference, thus giving you a better chance of approval.
Once you have finished and edited your dissertation, make a list of the basic points and concepts of your research. This will help you create an organized and memorable presentation. An easy way to arrange your presentation is to dedicate one or more note cards to each important concept you wish to discuss during your presentation. Writing a specific heading on the top of each note card will help you order your presentation in a clear, natural manner, while still allowing you to remember specific points you wish to discuss.
Your presentation will most likely be a positive experience, but is technically considered a "dissertation defense." You will encounter a lot of questioning that you should be prepared for. Review your presentation and after every section make a list of questions that your committee may ask. These could be questions about how you did the work, your research process, or your research findings. Take the background research that you did on the committee members into account when anticipating their questions. Write specific answers to each of these questions and practice these answers well enough to remember them should these questions be asked.
Many dissertation candidates are nervous about speaking in front of several people, so gain confidence by practicing your presentation in front of anyone who is willing to give you constructive criticism. This can be a friend, co-worker, fellow student or family member. Seek out a faculty member or former professor whose advice you trust and ask him to critique your presentation. This will help you get used to your presentation, point out any problem spots, and anticipate any questions, comments, or general problems you may run into during the dissertation defense.
To feel confident and relaxed on the day of your dissertation presentation, get a full night's rest. Wake up at a reasonable time, eat breakfast and go over the notes you have made in anticipation of your presentation. Arrive 15 minutes early, so the committee is not left waiting for you and you have time to become comfortable in your surroundings. During the presentation, speak at a normal pace, making an effort to speak slowly if you hear yourself speeding up out of nerves. Take natural breaths and regular pauses after discussing key concepts. Make eye contact with your committee members. They expect you to be a little nervous, but make a conscious effort to appear confident about your knowledge of the subject.