My characters surprise me constantly. My characters are like my friends - I can give them advice, but they don't have to take it. If your characters are real, then they surprise you, just like real people
Never argue with your characters; they know themselves better than you do
Two things I do well in books are sex and violence, but I don't want gratuitous sex or violence. The sex and violence are only as graphic as need be. And never included unless it furthers the plot or character development
When sex is necessary for the plot of a book, or a character development, then I don't shy away from it. Why should I?