Plan out the entire story in advance, and make sure you spread hints (or implications) of the major reveals throughout the story, because the worst thing is if the reader feels like the ending or the twist is half-assed. You need minor reveals as well; you should be revealing impactful information like a slow drip--each individual piece of info could be a crumb about the world, the characters, or the events that transpired, but the important thing is to give small crumbs over time so that it doesn't feel jarring. You want a story that is well-contained, flows well from the beginning to the end, but also completely flips the perspective that the reader started with in the beginning by the time the reader gets to the end.