One common weakness on both private and commercial check ride is the lack of precision control of the aircraft. I've noticed with both airplane and helicopter applicants. What it all boils down to is not knowing what aircraft attitude and power results in the desired outcome and/or not looking out the window.
Watch a pilot on take off. Does he establish a pitch attitude that establishes Vy or does he chase airspeed. If you take away the attitude indicator and ask for a steep turn, does the pilot have a problems holding bank and/or altitude. If you watch the pilot eyes, how much time does he spend looking inside the aircraft vs. outside. I would argue for VFR maneuvers the pilots eyes should be outside 85 to 90 percent of the time.
What about coordination? Does the airplanes nose slide inside or outside of the turn? Does the helicopter pilot make trim adjustments as power changes occur or after?
All these issues can be easily solved with the aid of the instructor. Show the pilot the correct attitudes and power settings. Use coordination exercises. How does each maneuver feel? It should be comfortable!