Best way to impress in flying grading is to do a few hours of basic instruction (good quality) first.
The grading takes the form of about ten one hour flights. You will NOT be required to take off or land the small "grob" aircraft. The flight grader (a senior instructor) will fly you out to the training area and then demonstrate a manoeuvre and ask you to fly the same. It starts off with the easy stuff eg straight and level and works up to more complicated stuff eg steep turns etc.
Just relax and enjoy the flight. Do try your best and if you stuff up one exercise try to do better on the next. What they really want to see is someone that can learn.
Best of luck.