Best advice is - sandbag at the cert a bit. Don't go 110% percent during the WoD's, may be 80% or so. It's not a CF Games qualifier, it's a place to learn.
Because if you do push really hard - you'll be sweating, cramping and having the hardest time remembering and writing down parts of the lecture and having a helluva time trying to hold the bottom of a squat/deadlift etc.
But you don't need any extra training prior to the cert.