Just make sure that whatever weight you're doing, that you choose a weight where your form is spot-on the whole set. My rule of thumb I tell myself is: light enough to keep my form perfect but hard enough to be making faces on the last couple reps .
Go lighter than you think and do a couple reps, keeping your form in mind. That will usually give you an idea of how you need to adjust and hey, you just got a warm-up set in!
Good luck, can't wait to hear how it went!