The first: record the year, not the day
The wedding is the most photographed day in most people's lives. The year afterwards is undocumented.
Paper, tin, silver, ruby, gold. The traditional list is more useful than it looks, because what each year is short of genuinely changes.
The traditional anniversary gifts get dismissed as arbitrary Victorian invention, and some of them are. But the list is a surprisingly good prompt, because paper at the first anniversary points at exactly the right category, and tin at the tenth, meaning something that bends without breaking, is a more accurate description of a decade of marriage than anything else on offer.
What actually changes between the years is who the anniversary is for. A first anniversary is private, and the useful gift records a year nobody documented, as opposed to a wedding day that was photographed exhaustively. A tenth usually arrives in the middle of the hardest decade, with young children and no time, and the gift that lands is logistical rather than material. By the twenty-fifth, the objects have run out and the personal has decisively overtaken the expensive.
From about forty years the anniversary stops being about two people at all and becomes about the family they produced, which is why those are almost always organised by the children rather than by the couple. And by fifty, some of the most valuable things are time-limited: photographing every generation together, recording the couple talking about how they met, and writing the names on the back of the old photographs while somebody still knows them.
One correction worth making early, because a lot of families discover it while planning: a golden wedding does not come with a card from the King. That threshold is diamond.
The wedding is the most photographed day in most people's lives. The year afterwards is undocumented.
Ten years in, the shortage is time alone together, and the gift is usually the organising.
Three things at a golden wedding cannot be done later, and everything else is decoration.
One sibling decides, everybody contributes something that is not money.

By forty years the gift is almost never for the couple's benefit. It is the family saying something out loud.

Twenty-five years in, the traditional list has run out of road. What to give a couple who have already been given everything, twice.