Sounds basic, but maybe bring it up in conversation?
Maybe that's the problem -- Sex is such a taboo in some circles, that even engaged couples don't bring up the topic.
For our marriage we had a very good priest (Fr. Timothy Pfeiffer -- not to be confused with his brother, Fr. Joseph Pfeiffer!) and he really did his job in this area as well. You could tell he wasn't comfortable talking about such things (e.g., describing what is licit within marriage and what is not), but there's nothing that man wouldn't do to execute his priestly duties faithfully and well. I still admire him for it. He is a zealous apostle. We were blessed to have him as our priest for 1 year.
He also had us read a good pre-Vatican II book, "The Catholic Marriage Manual" which covered a lot of subjects that trip up many couples and destroy many marriages: sex, in-laws, money, discipline, you name it.
It gave us, while engaged, some useful profitable topics to talk about. Fortunately, we were on the same page in these areas. But it's not quite that simple. We also learned a thing or two. To this day, I still have a healthy caution for "in-law interference in a marriage" since reading that book. It's good to know where the dangers lie, so you can be cautious.