Why is being a good son-in-law such a big deal?   Well, statistically speaking, we see a significant drop in the divorce rate when men get along with their wives' parents, especially their fathers.   But even more importantly, it affects kids.  Grandparents are very important to a child's sense of well-being because they can add depth and security to the loving relationships in his or her life.  The better your relationship is with your in-laws, the easier it is for your child to grow close with them and have more positive role models. 
 
For these reasons, I recommend that people think seriously about potential in-law problems before they consider marriage.  If you're walking into a situation where your future in-laws hate you, you may want to rethink whether or not this match is right for you. 

Losing family connections is bad for everyone involved, as I learned all too well from my own parents.  My mother was a war bride from Italy, and my father was a nice Jewish boy from Brooklyn.  My dad's mom did not like the fact that he had married outside the faith, even though the only thing Jewish about his family was that they were culturally Jewish and celebrated Passover and Yom Kippur.  My mother also didn't speak English very well, which made my mean grandmother all the more vicious.  She used to call up my mom almost daily saying how she wished my mother and me were dead.  It was a source of great strife in my family.

The less familial the connection is with your in-laws, the less happy, secure, and supported your marriage is going to be. Period.  That's why I advise couples to do at least six months of premarital counseling so they can cover these kinds of issues before they get married.     
   
So, assuming your in-laws are reasonable people, here's a list of things for all you men out there on establishing a good relationship with your wife's parents:

• Respect their daughter and take good care of her.  I am not the mother of a daughter, but if I was, I'd be in the face of her future husband saying, "You'd better take care of my baby.  Treat her with respect, love, and protection.  The most important thing to me is that you don't hurt her and that you make her happy."
• Be there when their daughter needs you.  I've heard too many stories about men who were too busy doing one dumb thing or another and missed the birth of their child.  If you're not at the hospital with your wife when your baby is born, you'll be missing out on a lot of great parent-child bonding.
• Act and look like a respectable man. If you want to have a meaningful relationship with her parents, act like a real man.  Don't look or behave like an idiot. 
• Reach out to your father-in-law.  The relationship between a father and a daughter is special. It will mean a lot to your wife and your mother-in-law if you can build a relationship with your father-in-law.  Find things that you have in common with him and go from there. Invite him to a ball game, go with him to a local event, or simply take him to lunch. Just spend some "guy time" together.  And if you aren't married yet, be sure to ask for his daughter's hand in marriage before you pop the question. This is a show of respect that he will appreciate.
• Attend family gatherings and engage. Don't be frivolous about not attending family gatherings.  Unless it's unavoidable, never let your wife and kids go to a holiday gathering at her parents' house alone - you are missing a fantastic opportunity to build upon your relationship with your in-laws and the extended family through conversation and a shared experience.
• Build good relationships with their other children. Try to connect with your wife's siblings and their
• Consult with your wife on how to handle sticky situations.  If it seems like there's a growing issue, consult with your wife.  She knows her parents better than you do.  If you think a situation is a little sensitive, ask her for advice on how to respond.

Above all, treat their daughter like a queen and not like one of Henry VIII's wives you're going to behead.  Simply put: be nice.  It doesn't kill you to be nice, does it?