Advice to parents is usually about teaching kids life lessons, how to be independent, how to interact and get along, how to cooperate and collaborate, self-control etc.
Lessons and traits which people need to be married and need to be reminded of and remind themselves of constantly during marriage.
Take this quote from Blessings Of A Skinned Knee: “Plan nothing- disappoint your kids with your essential mediocrity and the dullness of your home. Just hang around your children and wait to see what develops.” Just change it slightly, to “Plan nothing- disappoint your spouse with your essential mediocrity and the dullness of your home. Just hang around him or her and wait to see what develops.” and it applies to marriage.
The seven essential virtues, from Building Moral Intelligence – The Seven Essential Virtues That Teach Kids to Do the Right Thing by Dr. Michele Borba, Ed.D are: empathy, conscience, self-control, respect, kindness, tolerance, and fairness. Those are traits needed to be a good husband or wife and to be and stay married.
Of course, there are more traits than those needed, but the point is that if/when you read parenting advice you can also apply it to yourself as a spouse and to your marriage.