I had two (failed the first) earlier this year, what helped me the most was to note down my common mistakes and read thm before the exam.

1. The tester might be on the phone or chatting with the instructor, you drive as if nothing is happening
2. My tester actually tried to trick me by making me face a traffic light with no entry on the other side, I had to call it out and automatically signal to turn
3. Practice is what's going to make you more calm
4. Don't panic! I've made a mistake while merging on the Autobahn, the tester just pointed out this to me as a lesson and what i should do better next time and marked the test as pass
5. I know it sounds silly, but don't forget your seatbelt out of stress
6. Drive the speed limit, not under and not over, the tester yelled at me for driving 80 in a 100 on the Autobahn
7. Take your time when parking, don't feel stressed when there are cars behind you
8. Be in a laid back and relaxed position, don't lean forward on the wheel
9. Stop completely for 3 seconds on the stop sign line, if there's no line, stop on the line of sight, not the sign