I’ve only done a handful of jams (I think this one is gonna be my… 4th). There are a lot of ways to look at it, but one advice I can give you (and I wish I knew in my first two jams) is: aim small! 72 hours seems like a lot of time, and you will probably have a lot of good ideas, but believe me, you won’t have time to implement half of what you think. Aim for a single core mechanic, and build around it. Make sure you have a proper game loop (i.e. start, play, end, retry), then add more stuff or refine if you have time.
In our first two game jams, we had a lot of very cool ideas and a vision of what it would look like, but in the end, we were only able to present half-baked, incomplete and confusing “games”. The last one we did (the one I linked in my other post) was our first “finished” game. It’s simple, a bit rough around the edges, but at least it feels complete.
Good luck to you, a game jam is a very thrilling (and humbling) experience!