I recommend starting with Red Square because you will have morning sun on the front of St. Basil's. If you go in the afternoon, you will need to take your picture in an ugly parking lot on the other side :-). From here are several museums, Lenin's tomb, and GUM. It's not far to the tourism entrance for the Kremlin or on another side, the diamond fund, which could be your second and third stops for the day. Yes, it's a powerful, impressive and beautiful place today. If you truly want to appreciate this place, take a moment to appreciate how far Russia has progressed. Take a moment to understand the violence and sorrow that many generations felt here. A guide is highly recommended.