Since it sounds like you are doing a live presentation, where you will be working with real systems and not just charts (PPT, Impress, whatever) make sure it is all working just before you start. It never fails, if I don't try it just before I start talking, it doesn't work how I expected it to. Especially with demos. (I'm doing one on Tuesday so I can relate.)
The other thing that helps is simply to practice, practice, practice. Especially if you can do it in the exact environment you will be presenting in. That way you get a feel for where you need to be so as not to block the view for your listeners as well as any other technical gotchas there might be with regards to the room setup or systems.
