A few Grand Canyon notes....
The south rim of the grand canyon gets VERY crowded in the summer...but there are some ways around SOME of the crowds. The worse crowds are often at the overlooks at sunset and the return shuttles...but that's one time you just have to suck it up and deal with the crowds...the sunsets are worth it...remember to look toward the EAST too at sunset time...that is often the nicest view.
My favorite thing is to hike the west rim trail. I like to leave soon after sunrise. You won't be alone but the huge crowds won't be there until later in the day. Plus, its cooler first thing in the morning and you'll see some wildlife.
The trail is easy but take plenty of water and snacks. The nice thing about this trail is it goes between the major overlooks....while much of the trail is away from these oasis's of humanity, you always have the option to opt out of the hike and get on the shuttle bus at any of the overlooks if its too hot or someone gets tired. This way you can hike as long as you like without worrying about getting back. At each shuttle stop just make sure you have the stamina left in the tank to get to the next one. Some of the stops are relatively close together while others are over 2 miles so watch your map.
Also, take the Bright Angel Trail below the rim. My knees don't allow me to go far but just 1/2 mile puts you in a whole different world. Unless you are a hardened athlete it will take 3 times as long to come back up as it does to go down so avoid getting stuck down there in the heat of the day.
Enjoy....