As Ian says, the hardest part is directing, and the first time I did any form of professional shooting I was a complete wreck, but what I tend to do is sit down and ask them if there are any particular shots that they have done before that have come out well before, and see if we can revisit, there's also the advantage of trying things out and experimenting, and always have a few magazines on hand from the likes of FHM or Esquire or other catalogues to see if they happen to like certain styles.
Always give them room to breathe, joke around a little, make them comfortable and well yup there are certain poses that some people get into that are somewhat... revealing or provocative, so you just make a joke of it, also helps to have a friend there (not for them, for you!)