London is such a large city and there are many attractions to see and visit. What a visitor wants to see depends on him or her. The following is a very long walk I suggested to visitors, who seemed quite happy, if exhausted, with the route. This route took them to the places mentioned in the title.
According to Google maps, the whole thing is 4.13 miles long. It takes a good few hours and it is not suitable for those who find it difficult to walk or don't like huge crowds. You are unlikely to have the time to enter museums and galleries with this walk, so it's really aimed at those who like to see the exterior of the famous buildings and gain a feel for the city.
This walk starts at Leicester Square tube station (but can start at Embankment) and ends at Marble Arch tube station. There were two things that determined the order and route: (1) seeing the Changing of the Buckingham Palace Guards at 11:30, and (2) lunch in Chinatown. They started just around 10:15 AM and had a plenty of time before the changing of the Guards started.
View London walks (1) in a larger map
This route can be expanded to include Westminster (the Parliament Square) or shortened by excluding Oxford St, and I'd really welcome any suggestions, glosses or comments regarding this route.