Take an interest in getting to know your future daughter in law, in meeting her family. Invite her parents over for a casual (less stress) meal or to join your for breakfast, lunch, a casual supper at a restaurant. You pick up the tab.
Be clear about how much financial help (if any) you will give the young couple with paying for a wedding, a honeymoon, with setting up housekeeping together. Along with that be clear about what you expect in return.
Let the couple know early on if there are people you'd like them to invite for you. If they're paying for the wedding themselves, you may have to accept that your favorite cousin won't be invited. But if you're making a significant financial contribution, then you might want to make that conditional on being allotted a certain number of guest slots to fill as you please.
If the couple makes a choice you don't like, a choice like "adults only" or "no dates, serious couples only" then support them in that choice. Or at least don't undermine then by making your disagreement public. Put aside ALL family squabbles; your family should be presenting a united front to the bride's family and to the public.
Be prepared to answer questions like "What gift might the couple appreciate?" and "How dressed up should I get" in the way the couple would wish you to answer such questions without volunteering your own views on the wisdom or appropriateness of their wish list, their dress code. It's not YOUR wedding.
It's an old custom for the groom's family to host the rehearsal and a rehearsal dinner. Discuss with the couple whether you will be following this old custom, what exactly your are or are not willing to do. For example a rehearsal can be restricted to only those with something to rehearse or can include parents, attendants' spouses, the couple's siblings, out of town visitors, or whoever you'd care to include. For example the rehearsal dinner can be as simple as a cold cut and veggie platter you bring to the rehearsal place or as lavish as supper at a luxe restaurant.
At the ceremony and celebration, subordinate your own desire to have a good time to your helpful impulses. Help the couple accept gifts and keep track of who gave what. Rescue wall flowers and make introductions. Dance with the ladies. Be alert and do what you can to make the party a success, to relieve the couple of stress.
If you want to go "above and beyond" then offer to help the couple with their thank you letters.
Be understanding when your son starts doing some things the way his wife's family does them instead of the way he was brought up. For a marriage to succeed it must be a blend of both family's ways of doing things, not everything in the way your family does them. For example if your son asks you to stop coming over without calling first, then do that.