Your tips Buy daily tube passes - by far the cheapest way to see London (includes buses). Plan what sights you want to visit - there are so many, and you don't want to miss any out. You MUST go to a West End theatre production.
I have been to London 5 times, and cannot get enough of it. We have still not seen so many historical sights. We love the theatres, the Buzz, Covent gardens, Hampton Court palace, the bus tours, and just being there. It feels like a second home, and cannot wait to go again.