A London first-timer guide for royal sights, museums, river walks, transit choices, and neighborhood pacing.

Westminster Abbey, Parliament Square, St James Park, Buckingham Palace, and the river create a clear first London route with royal and civic history.
The British Museum, National Gallery, or Tower of London can each become the main interior visit. Trying to stack them all usually flattens the day.
Keep an indoor alternative and a Tube/bus buffer. London rewards flexible sequencing more than rigid sightseeing grids.