I have been doing the same thing over the past few months as the practical element of an English as a Second Language course.
A dress rehearsal is a good idea (which I have not been doing myself). I did have to rehearse one exercise insofar as, having thought of it myself, I had to work out how to do it. That worked quite well.
The rehearsals (in front of cooperative peers perhaps, to make it realistic?) both highlight aspects you may be less than strong in, and allow you to "tune it in", so that you can do it without thinking too much.
Another good idea is to finish all preparations ahead of time. Being ready to go a couple of days before gives you leeway to deal with last-minute hitches. It also lets you put the practical out of your mind until the time comes.
