We are two 60 year olds (husband of 38 years and myself) and this was our first trip to London. We had originally hoped to travel during the last two weeks of May to both London and Paris, but emergency surgery got in the way so we had to re-book for just one week in London.
My first tip -- Get travel insurance. I didn't lose a penny on re-booked flights and pre-paid train trips and B&B deposits from our original arrangements.
Anyway, we took an uneventful night flight from Washington, D.C. and landed in London around 10 in the morning. Immigration took about an hour.
I had originally thought we could get by with just carry-ons but ended up with two 26" and one carry-on. Decided to book the Heathrow Express train, which is very easy to find at Heathrow, and got to Paddington Station in about 15 minutes. At Paddington, I purchased our 7 day travelcards, and we used the tube to get to Pimlico, the closest tube station to our hotel (Mint Westminster) next to the Tate Britain. We used several of the 2 for 1 tours and restaurants, and thought the Travelcard was a very good deal.
Although the tube is cheap and fast, I was only able to get a seat twice the entire time we cris-crossed London all week. The buses were much more comfortable, but with so much construction, certainly slower than the tube.
Tip -- Keep a handful of change for public restrooms at the tubes. They range from 20 pence to 50 pence.
Tip -- Get tube and bus maps before you go, and map out the routes before you go out the door in the morning. When you get down in the tubes, it's loud and crowded, and there are always other lost tourists crammed in front of the map.
All week I used the ATMs exclusively and paid everything but our hotel bill in cash. I had no problems at all.
As I mentioned, we stayed at the Mint Hotel Westminster. The hotel is very modern, with an iMac and free wifi in every room. Although small by American standards, the room was spotless and very quiet on the 9th floor. Every night was a different price, but it ended up being about $250 USD per night for a standard room with king bed.
I was concerned that it was not closer to shops and restaurants, but in the end, I was glad we stayed there. If you make a left out of the hotel, there is a sandwich shop about a block away on the left and another cafe, "The Rocks", another block away on Vauxhall Road. We never paid more than 8 -10 pounds each for breakfast, including the platter sized "full English breakfast" and orange juice. The Pimlico tube station is maybe 10 minutes away. Westminster tube is perhaps 10 or 15 minutes in the other direction.
During the week we took the Big Red Bus tour and a cruise on the Thames. We also did several LondonWalks tours -- Tower of London, British Museum, Westminster, Legal and Illegal London, Spies and Spycatchers, Ghosts, Gaslights and Guiness, Victoria and Albert Museum, and an out of town walk to Oxford and the Cotswolds. We enjoyed Brian, Richard III, Adam, and the guy with the green carnation. The lady guides were OK, but not as animated.
Tip -- Buy their discount card for 2 pounds that you can use for up to a month and save two pounds on any tour.
Tip -- If you want to go to the Tower of London or Westminster Abbey, do it with Londonwalks. They get a small discount on the admission prices, but you also get to skip the long, long line of people waiting to buy tickets. After the tour is over, you don't have to leave immediately.
Tip - If you want to have afternoon tea and don't want to dress up or spend a fortune, the Orangery at Kensington Palace is casual, and a huge piece of Queen Victoria Sponge Cake and tea was about 6 pounds.
My favorite tour was one that we did ourselves at the Churchill War Rooms. We spent almost three hours there, and it was just unforgettable. That was one of the 2 for 1 tours.

You could spend a month in London and not see everything, but we walked till we dropped every day and saw almost everything -- Didn't make it to the British Library, Harrod's, or Kew Gardens, and we didn't see Kate or Pippa, but still had a wonderful time.
Thanks again to everyone who helped with my planning.