Raft it if you ever get the chance. The canyon walls rise up as you go downriver, so it’s almost like you’re starting at the top and working your way down, except you’re on a raft floating along with a cool drink in your hand or you’re running rapids. You camp out on beaches, have sumptuous meals (for camping, anyway), take any number of hikes, it’s really incredible.
Besides rafting, I thought a great sense of scale came from hiking. You get the grand views from the rim, but you really need to get down in there to get a feel for how vast it is. At least get down off the rim and away from all the people.
My wife and I went for a 10 mile hike on the North Rim, cleaned up at the campground, walked over to the lodge and devoured huge juicy prime ribs, baked potato, bottle of wine, the works. Then we walked back to our little tent, crawled in, and passed out. That was a great day!
There’s also the mule option, which would be a good way to go if you want to get into the canyon and are short on time or don’t feel like doing the hike.
A few practical considerations, since you didn’t mention details like time of year…
If you’re planning a winter trip, everything on the north rim will be closed. The south rim gets a significant amount of snow in the winter, but stays open.
If you’re planning a summer trip, traffic at the south rim gets awful. Going to a nearby town and taking a bus works well, or staying at one of the hotels there and traveling by shuttle for the entire visit.
Plan on early morning hikes. It’s cool and pleasant and the scenery is spectacular at dawn. It’s also less crowded then. On our visit last month, we saw a bighorn sheep from an overlook just a couple of miles from where we were staying.
If you’ll be hiking there in the summer, take water. Lots of water. Dehydration is the #1 problem with hikers in the canyon. You do not want to be medevac’ed out for having a heat stroke in the canyon. On top of everything else, you’ll have to pay for the medical helicopter, which ain’t cheap.
If you want to eat at one of the sit-down restaurants, make reservations well in advance.
If you want to explore the canyon floor, don’t plan to hike down and back up in the same day (unless you’re in very good shape and you can make brisk work of that one-mile vertical climb in the evening).
The mule rides are limited to people under 200 lbs. If you’re a big guy like me, it’s disappointing to get there and find out you can’t go
Take along a small flashlight in case you plan poorly and end up not getting back by nightfall. When it gets dark out there, it gets dark!
There are places you simply can’t go by car, including the new visitor’s center. Check out the shuttle maps when you get there.
Oh, one other thing I forgot, just to make sure your expectations are realistic: The Grand Canyon is not a theme park—it’s a National Park. There are steep trails with no guardrails. There are places where you can walk out on a rock and look down a cliff thousands of feet tall. There are mountain lions. It’s a wonderful, beautiful, incredible place and it has real, live dangers.