I had the advantage of being offered a mock oral RT exam by another controller. It cost me but was worth it.
As part of the exam, you are given 10-15 minutes (can't remember exactly) to prepare. In this time, write down on a piece of paper the order of things for a MayDay. Also write down the points at which you plan to make various calls.
OK, things to remember:-
1. Press the button to talk!
2. Change frequency on the dial machine!
3. Don't abbreviate your call sign unless the examiner does so first.
4. The MayDay will be near the end of the route
5. Within reason, you can take as long as you want - you are flying from A to B and in reality that could be an hour long flight!
6. Take a glass of water in with you.
7. The route you are given will probably be fictitious.
Good luck
Cheers
Whirlygig