@kmarie719: If you’re going in December, the North Rim is going to be closed (you can still visit, but services are closed). The South Rim, also known as Grand Canyon Village, will be open.
ETA I see you said South Rim!
If you’re in any kind of shape, you can hike down a bit to get some different vantage points. Bright Angle and Kaibab Trail are popular. I did an 8 hour hike out to Plateau Point through Indian Gardens Campground. That was 3,000 vertical feet. Remember you’re at 8,000 feet on the South Rim. It could be snowing or icy! It was 22 degrees in the AM when I camped there one May.
Here is the official GC NPS link
Here is a link to stuff you can see and do. There are ruins, museums, scenic drives, hikes, ranger talks, etc. I recall Tusayan Museum and Ruin that had a 3,000 year old “toy figurine” on display. I thought that was impressive. I like seen ancient Indian structures too. The Watchtower you can climb up to get panoramic views.
Since Grand Canyon Village is kind of far from everythig else. Not sure if you planned on staying IN the park or not. Williams, AZ is 1.5 hours away. It’ll will be getting dark at 5pm in December, so you could drive back to a real town in the evening if you wanted.
So in summary, if you don’t do any hiking at all (except for some strolls at the rim), this would be very much a drive, park, and get out and look at something, repeat kind of trip that you could do in one day. The park newspaper you ask for upon entrance does have suggested itineraries, if you have 1/2 day, 1 day, couple days. Or you can ask the ranger for their input. I don’t know of any “secrets.” I do for other parks!
Let me know if you’d like more info!