I was told by someone does the sim evals at CAL that outside of the obvious "can he/she fly ?" They are looking at how you deal with a mistake. They know that nobody will fly a perfect ride. Almost everybody gets 50 ft high, 5 kts slow, one dot off the loc etc once or twice during the ride, what they are looking for is that you notice and correct the error in a timely manner. If you do that your fine, where people run into problems if you dont correct your errors, make them repeatedly, or let them ball you up.
If you make a mistake and then start worrying about it, it will affect your flying for the rest of your ride. At CAL the majority of people have no problems with the sim, it is set up for you to pass.
The best advice I could give anybody is to go and start working on random holds so you are fresh on that because lets face it you never really do it any more. And do a Sim prep especially if you are coming out of a Glass airplane, it takes a little while to get comfortable with a round dial airplane again.