A lot of people fail on the private checkride because of forward slips, slow flight, and short field landings (being afraid of controlling the airplane at slow airspeeds).
Also, a lot of students seem to think that high density altitude is good! It's just the opposite. High density altitude is very bad! Also, know that the engine will continue to run even if the battery dies during flight! That was a problem that plagued my private checkride!
Boyd from the U of I in Illinois got me with that last question, but I still consider him a fair examiner if anyone wants to do a checkride with him. In fact, he actually turned out to be one of the nicest and most fair examiners I have encountered yet.