I think Ken Sande's The Peacemaker has probably the most important practical thing: a way to solve disagreements and problems when they come up in such a way that short accounts are the rule of the day. If both are Christians, then they can commit to keeping short accounts, working through issues, and prevention of long lists of faults being used as weapons to throw at each other. As some wisecracker said, "When my wife gets mad at me, she doesn't get hysterical, she gets historical." Prevention of this and of the "You always" and "You never" traps are fairly key to a healthy marriage. I spend more time on this in marriage counseling because it seems to be the hardest thing for couples to work out.