Do not prepare a plot. You are not an author writing a story. You want to prepare an interesting world and an interesting situation, and the plot happens when your players interact with it.
I highly respect this bit of advice. It's a classic. But I have also found it can assume a certain kind of player, and that there do exist players which seemingly desire a storyline they can just follow. They still want to have agency and make interesting and consequential decisions, but I still find them a bit aimless and lost when I drop them in a sandbox.
In fairness to this received wisdom, I think the phrase interesting situation is doing more work than I have historically given it credit for. It's not just about it being interesting in the abstract, but (at least with some players and parties) presenting a status quo and then introducing (or threatening) the prospect of changing that status quo. I suppose my tl;dr is that with interesting situations inaction should feel like a meaningful choice. The orphanage will burn down, the criminal will escape, the freedom fighter will be caught. (Ideally, you leave the determination of whether they're a criminal or a freedom fighter up to the players.)
You can still have an evolving story happen and it’s not about the player building that story. But the story results from the choices they make in the situation you present.