One of my favorite resources is The Respect Dare by Nina Roesner. This is a 40-day challenge to help you explore the concept of respect in marriage. This is a woman’s resource, but men might find it helpful as well. It might even be something couples could work through together.
My other thought is Choosing Civility by P.M. Forni. It’s explores a number of thoughtful behaviors (including respect) that make for healthier, happier relationships. Wouldn’t marriages be amazingly wonderful if civility was a cornerstone of relationship?