Wind it all the way out, go ride, keep winding it in untill the fork feels ‘stable’.
I always found it was a lot harsher than I first guessed.
The rebound has a similar effect, so the more compression you wind on, the more rebound you can add as it’s using less travel for a given impact, so needs to rebound less, which makes it even more stable. In spain (big, long, fast, rocky decents) I fiddled with them until they felt right, but they also felt very harsh, untill we videod them and it showed they were doing a lot of work, I was just hitting things faster and they were absorbing a lot of impacts.