We did the Keys to the Kingdom tour last November and loved every second of it. We had an 8:30 AM tour time so we were able to enter the park before it opened and got some amazing pictures of an empty Main Street and Castle. Here is a little overview of our experience:
We got up extra early so that we would be at MK well before our scheduled departure time. Once we got to MK we went off to the right to see a very nice lady with a clip board who asked us for our tour information and names. We then got to enter MK before park opening and immediately went to the Guest Relations Lobby in City Hall. They asked us our names and what we would like to eat at lunch. Then we got our audio packs, name tags and were told to meet our guide just around the corner in a few minutes.
Before we met our guide we were able to stand at the beginning of Main Street and get some amazing pictures of the Castle without all the crowds. Then we met up with our group (about 12 in all) and our tour guide (I can't remember her name but she was great!). She gave us an overview of what we would be doing, showed us how to use the audio packs and began our tour at the flag pole. While there, we got to listen to some interesting facts about Main Street and see the cast members walk the crowds in after rope drop.
I don't want to give too much away about what we did and saw but we began at the flag pole, then on to Adventure land and rode JC, then to Frontier Land and a little backstage action, some lunch, rode HM, then to the utilidors and back on Main Street. It was such a fun time.
I highly recommend wearing comfortable shoes, sunscreen and possibly even a hat as we were walking a lot in the sun. There are however, plenty of bathroom breaks and stops to rest as well.
Let me know if there is anything specific you have questions on!
Enjoy!