I'd say, keep as open a mind as you can. Don't go in there with any sort of chip on your shoulder, i.e. when the instructor tells you something you're doing wrong, don't let ego come into it - listen to what he's telling you.
I took a couple of lessons from a fellow last year, and man, did he find things wrong with my stance, stroke, etc. I did my best to stay open-minded - hell, I knew I had troubles to start with, it's why I hired the guy! - and just those few things he told me helped me quite a bit.
And just this past week, I had one fellow tell me one thing about my grip - and damn if he wasn't right, and it's been helping.