I remember many years ago, when my brother and sister-in-law had their second child a few years after the first one, when she was asked if she'd been surprised by anything in raising them, she said, "Yeah, I thought I could use all the things I learned in raising my first kid to raise my second, but they are completely different and almost nothing works the same with the second kid!"
I think that would be among the most important pieces of advice I would give my son about sex. Just when you think you have it figured out with one girl, and you try the same thing with the next one, you realize the knowledge is not transferable, and you have to start learning what works all over again. Well, except all that dumb stuff about communication and meeting each other's needs blahblahblah. :-)