I've found two common problems when teaching newbies. The first is when they standup too soon and wind up on top of the table. We just instruct them to stay crouched until they are out in the flats before standing up.
The second is when they do that see-saw motion, they fall back to the back of the pocket and then once they climb the wake come rushing forward. TYPICALLY, it's either they are too far back on the board, or they have that wakeboarder stance. This before-and-after set of Garrett exemplifies this: