What is the best itinerary to see London sites in 3 days

A guidebk would help so you can plan your museums ahead and routing. Ricks guidebks are excellent for ides and restaurant choices nr the sigs. Museums, Not all are free but many of the biggies are. Hop on and off can be pricey so perhaps walking most as u are in a gd loc at hyde park then take local bus to eye etc. pret a manager is a gd fast lunch type place and pubs are great fun for lunch and dinners at a reasonble price.

You'll get in plenty of walking in London. But to use your limited time most efficiently (there's so much to see in London), you'll want to use the Underground to get between major areas, as the attractions in London are spread over a large geographical area.

The State Rooms of Buckingham Palace are only open to the public in August & September. The Changing of the Guard (outside the Palace) are open year-round.

Many of the big museums are free, which makes them very popular with both the tourists and the locals (the locals on the weekends when they can bring the family), so expect them to be crowded.

London is one of the more expensive hotel towns in Europe.

Pub grub used to be a lower cost way of eating, but not so much anymore (for four people)--so allow an adequate budget for eating.

A good guidebook and detailed map will be helpful.

Walking is a great way to explore London if you have the time, with only 3 days, the Tube is a better idea. A walk from Hyde Park to Tower Bridge along the South Bank (definitely worth doing) is about 5 miles and will take around 2 hours, if you don't stop to look at/explore everything you'll see, could easily take all day if you do. If during the week, drop into Borough Market on the way for lunch. Small take away dishes that you can all share to get a good taste of lots of different cuisines... if you're into food at all.

Not the very cheapest, but good value overall is Carluccio's (Italian), if you do want more of a sit down restaurant. Relaxed atmos and good food. I still maintain their version of our "Full English" breakfast is the best, if not traditional. Many branches in London, St. Christopher's Place being one of the best.

I'd definitely do the open top bus day 1, assuming the weather is nice, allowing 3-5 hrs to do the basic routes, you will see a lot this way. Then once you've had an overview, you can cherry pick sites to go back to. Do the biggest ones at opening time, like the Tower of London.

Don't ignore sun cream if on the open top bus for a number of hours.

As close to Hyde Park, a walk through there is very nice, loads to see, you could easily spend a day there (don't though). An early morning "Full English" (traditional version) and a cup of tea in the Lido Café (the one near the Diana Memorial Fountain) next to the Serpentine is lovely.

Museums are mostly free, but with only 3 days, I wouldn't allocate much time to them, fantastic as they are. You don't need to be in London to see great museums, so make the most of things that you can only do in London. Museums can be saved for a back up plan if the weather is bad.

Book the Sky Garden (weeks/months in advance) for a free visit and save time and cash not doing the London Eye.

http://skygarden.london/

Pret-a-manger (British) is a great place for a snack on the go, and in comparison to most, very reasonably priced. Other good ones are Eat (British), Itsu and Wasabi (both Japanese), all have branches everywhere. Good fish and chips is hard to find in my opinion, and the proper stuff (fresh fish rather than frozen) can be pricey.

Hope you have a great trip.

To visit, Tower of London, St Pauls, Westminster Abby, British Museum.
if you are in London from Thursday onwards then visit Borough Markets.

Is this 3 full days or do these days include arrival and departure? The majority of the museums are indeed free but as noted unless they are must visits (ie. The British Museum to see Egypt) it would be best to plan your days without them. Hyde Park is very large so not sure which tube station will be closest to your accommodation. No matter. Once you are settled, have you Oyster Cards, ride the tube to the Westminster Station. Locate it on the big map in the tube station. Hopefully you'll not need to change trains to get there. At Westminster Mind The Gap, exit the train and follow signage to EXIT 1. Walk out into the light. The Thames will be in front of you with the London Eye across the river. Turn toward Westminster bridge and look up. Start your visit to Parliament Square there, viewing the iconic Big Ben and Houses of Parliament. This when you should visit Westminster Abbey. After a good hour in the Abbey, walk back outside and across the street to Birdcage Walk ( use Google Maps Satellite view to see where I'm talking about, type in Big Ben, London, United Kingdom.). Follow Birdcage walk thru St james Park up to Buckingham Palace. From there you can walk thru Green Park to the tube station where you can connect to other parts of London or merely take time to walk up Piccadilly. This is Day 1.
Day 2 up to you but I would see the Tower of London, get there when it opens, Tower Bridge, walk up to Leadenhall Market place for lunch (and if the teens are Harry Potter fans search for he entrance to The Leaky Cauldron), from there off to St. Paul's cathedral or if that's not on your must see list, board the tube again to Old Spitafield's Market......lots to see in London. Easy to group things together but best if you get the RS Guide Book which will help you do this. Lastly, I've never ridden it but yes, you could do the hop on and off buses. There's been much discussion and advice shared about them on this forum.
Enjoy your 3 days. Great city!

1. Realize you can't possibly see everything in 3 days.

2. Plan to wake up early on the weekends to beat the crowds and have the streets to yourself. This was the best thing we did our trip and I have lots of pics of empty London and the golden sunrise light reflecting on Parliament. If you can, get up at 7am and get going on a walking tour of Westminster. We started at Parliament, wound our way past Westminster Abbey, and made it all the way to Buckingham Palace before the crowds showed up.

3. The Tower and the British Museum will each take most of an entire day to see them thoroughly so decide now if that is how you want to spend your time. We opted to give the Tower a miss this trip due to limited time.

4. Plan your museums and see what exhibits are available so you can focus on the few that really interest you. We breezed through the British Museum to see the Rosetta Stone, Elgin Marbles, and mummies, then left; it was crowded and overwhelming. I enjoyed the special exhibit of portraits of the Tudor monarchs at the National Portrait Gallery a whole lot more and that was the only exhibit we saw while we were there.

5. Take in a show while you're there. We didn't have time due to meeting up with my husband's friends from uni but it is my biggest regret and one I plan to fix when we return to London.

6. Take time to stroll. Be it through Burrough Market, Covent Garden, Camden Market, or Little Venice, take time to just take it all in.