I went last year for a day trip and really enjoyed it. We did our own thing when we went and relied on the map they give you and a book we got before hand as we are not huge history people but wanted to see it. We didn't go on a tour, but they have plenty available if you're really interested in doing that.
I would get there as early as you can. There was a HUGE line to get in and I don't think we went on any particularly special day - I think it's generally very crowded, it took ages to get in.
Inside the Palace, obviously the Hall of Mirrors is quite famous and awesome. We walked around the entire inside I think (some of it is closed off, at least when I went, so the Palace itself is not daunting to cover). It can feel a little cramped inside with the crowds, but not as bad as the Louvre which was mostly miserable with the crowds
The best part were definitely the Gardens for me. We went on a gorgeous May day so walking around and seeing the various topiaries, fountains, lawns, statues etc were quite something and that is when you realize how massive everything is, and because it's so spread out, you don't have to deal with any crowd/people issues whatsoever. We had the Museum Pass but you needed a separate ticket to walk outside because they had a show that night - which was annoying, but still worth it. Good to picnic and have an outside lunch with too. The outside grounds are where it gets overwhelming. There's a few side attractions you can go into, including Marie Antoinette's Estate, and it is REALLY far apart. They have shuttles and things as it will literally take an age to walk around the entire area. Didn't go to the Estate but probably would if I went again, but I still felt totally fulfilled with the visit.
So, based on my experience, hard to break out a detailed itinerary (which I don't usually do when I travel too much either) but you can definitely see it all without a real game plan too. Not much else to do in Versailles itself besides the Palace as well. Totally worth it