When it comes to tours and such, I HIGHLY recommend Westminster Abbey's "Verger's Tour," (with a live guide -- an abbey verger) rather than any kind of self-guided or audiotape tour. The same goes at the Tower of London. The Beefeater's Tour is the way to go. These people generally LOVE their roles and love bringing history to life for you, so if you want a strong dose of English heritage and history, I recommend those two things. (A lot of people love going to Evensong at Westminster Abbey, but a more unusual thing is to go for Morning Prayer. I believe it's at 7:30 a.m., but if you go, you'll be one of a handful of people, and the others will most likely be employees of the Abbey. It's a totally different experience to enter the Abbey when it's empty and be led back to an small chapel that is the oldest part of the Abbey. When it was over, the priest showed my husband and me into the cloister and turned us loose saying, "You're seeing things most people never see." We just wandered around and watched the students rushing into school in the uniforms -- shades of Harry Potter without robes! -- etc.)

A good way to spend your first day (trying to stay awake, if you arrive early morning like most of us do) is the Hop-on/Hop-off bus that has already been recommended. Sit on the top so you're getting lots of sunshine and fresh air -- important if you're trying to stay awake! -- and hop off frequently to walk a bit, just to keep the blood flowing. You'll get a good feel for the lay of the city and have lots of opportunities to just soak in the atmosphere, and plan what you want to come back and see later!

Have a blast!