Three Days in London

As a first timer visitor take the time to get and read the RS London guidebook.

Filled with very insightful intel that will help you decide (based on your interests) what is important for you to see.

Loads of places to eat. Nandos, Dishoom, Pret a Mangers, Pub grub, Wahacas, street market stalls, etc. Again, all about what type of food you seek. You can even have a meal in the crypt at St Martin in the Fields near Trafalgar Square.

This link provides good descriptions of various London neighborhoods. https://www.google.com/amp/s/matadornetwork.com/trips/quick-travel-guide-neighborhoods-london/amp/

See what sounds good to you.

Great city to explore. You’ll only scratch the surface in 3 days. Lastly August is the height of tourist season. Crowds will be massive.

Here's lots of good advice from our host about sightseeing in London. Check out a guidebook or two, see what most interests you, and plan your days around geography. Guidebooks will have hotel recommendations, and booking.com is a good search engine that lets you filter by location, cost, and various features. When you've identified hotel candidates, try to book through their own websites. London is so spread out that there's no "central" area for sightseeing, therefore no ideal location for accommodations. Anyplace within or near the Circle Line tube will be close enough, the tube is easy to use to get around.

So much would depend on more information about who you are and what it is that you like to do. With so little time, it might be nice to use one of the Hop On Hop Off bus tours, so you can see the sampling of the big sights, then decide which ones you want to see more closely, and hop off for those. I found it was helpful to set up some kind of connection with people, I had a friend who lives there, and I stayed at the Girl Scouts' hostel Pax Lodge. Good way to immediately have a network. Even if all you do is join a MeetUp.com group, you might be able to make a connection with an event or new friend for a pub time.

Also, You Tube has lots of videos that show the basics about how to get around in London, how to ride the bus system, the Tube, lots of different skills.

I personally like the idea of getting a hotel like Travelodge.co.uk as close to Paddington as I can, so I can take the express from Heathrow and get into London as quickly as I can, after a long plane ride that I may not sleep on. I know how to navigate the bus system pretty well but I'm thinking of doing the Hop On Hop Off next time to get more of a tour and to avoid some crowds.

The other thing I want to do on the next trip is to get on to a boat ride tour, there are so many historical buildings on the Thames, it would be kind of nice to know what they are.

Always bring a small pair of binoculars, useful outside and inside castles, in stations, airports, lots of ways.
I'm from New York (downstate) and the highlights in NYC can be seen in a week, but London would probably take more like 6 months, so it's really up to the travelers to identify what it is that they want to see. The HOHO bus tours could give an overview of the biggest sights, and you'll have time to identify what else you'd like. Personally the visits to Windsor Castle and the British Library's Treasure Room were real highlights, Trafalgar Square in the summer with the fountains, and along the Thames on the South Bank to enjoy the summer fair and festivals.

Just get real specific about what's fun for you, and do it :)

Alison makes a good case for a HOHO bus as a way to get an overview of a city in a relatively short time, but don't confuse that with using the HOHO for basic transportation. If you know where you want to go, it's a slow, expensive, inefficient way to get there. Riding in a HOHO until you come to a place where you'd like to stop and linger means waiting, sometimes awhile, for the next bus before you can move on. I've taken HOHOs (not in London) in cities where I wanted to "see" a lot in a short time, but regular transit (tube and buses in London) is much faster, cheaper, and a worthwhile experience in itself.

There are lots of websites suggesting what you can do in 72 hours in London, so one of these would be a good starting point and quicker than reading a whole guidebook.

Staying anywhere within Zone 1 of the tube will give you access to the main sights. You don't say what your budget is - look at the Premier Inn chain for better value accommodation.

You don't say what your interests are, but I would suggest that you see at least 1 museum, 1 art gallery, take a walk in a park, visit St Paul's or Westminster Abbey, see Buckingham Palace, the Houses of Parliament and see a show.