Prepare to be stumped.

The SAT is designed to include some questions that the average student will have difficulty with. 

This means that even on your most confident day, with all the preparation in the world, you will come across questions that you are unsure of.  You may even go blank.  When this happens, take control.  Don't let the question ruin your confidence or send you into a death spiral of negative thoughts.  Instead, just think to yourself, “Oh.  Here’s one of the questions I don’t know.  I knew there would be some.” and then move to another question.

Hurdles will happen, so learn to expect them and pre-think your reaction.