Consent is a terribly important topic to discuss when talking about sex.
Some just wing it and hope for the best.
Having an honest conversation with a trusted friend can make a world of difference.
You can find out where they prefer to be stroked during sex, or how to do a cunnilingus or even an anilingus for the greediest ones.
Seeing as they're much more experienced than the teen couples they just so happen to run into, they often take advantage of them, too.
Instead of letting those items come up in the way you teach, take some time to make a list for yourself of potential negatives so you can avoid letting these topics taint the conversation.