If it is your first visit to London, get acquainted with major London attractions and historic sights:
Big Ben, Houses of Parliament, Westminster Abbey, London Eye, Covent Garden, St.Paul's Cathedral, London Bridge, The Tower of London, Tower Bridge, Buckingham Palace.
We drafted some sample itineraries if you are exploring London on your own:
You can also take a guided sightseeing tour. Or you can purchase a double-decker sightseeing, visit the attractions of your choice, and continue the tour with the next double-decker bus. It is very convenient, especially for the first visit. Also, there is a discount voucher booklet that will be provided as you board the bus, so you will be able to save on attraction admission tickets. There are several double-decker tours in London. We recommend Big Bus as they have frequently running buses, great quality audio narration in 13 languages, and very friendly staff. Learn more.
Their routes are well thought-through and are already an itinerary. If you are in London for several days, consider purchasing a 24 hour tour or 48 hour tour as in such case you will have more flexibility to explore more attractions.
If you decide to explore London attractions on your own, consider getting an Oyster Card. It provides good savings on using public transportation in London.
There are many other activities. Take a look at Things To Do for more ideas. For evening activities, please check Musicals and Shows and Opera and Ballet sections to see what's on in London during your visit.