First day in London

In addition to the Hop On Hop Off bus, defitley recommend going for a walk. You could walk around the main tourist areas- Westminster, Trafalgar Square, Big Ben (National Art gallery if the weather is wet), or along the Thames Embankment. None otf these are near your flat. If there was somewhere to leave your luggage at the flat you could try Hampstead Heath or London Zoo wjich seem reasonably close to Archway Tube

If you have not been to London before one option would be the Hop on Hop Off buses to give yourself an overview/familiarise yourself with London. You could sit on the open air upper deck. Another option would be the British Library which is only a short walk from St Pancras, they have restaurants/cafes. Also St Pancras itself is newly done up and has shops/restaurants/bars etc.

Kris,
How much time to you have to spend in London? Depending on whether you have much time or little time might alter my answer to how much you should attempt on the first day. Some people on this site have reported falling asleep on the hop on/hop off after a long plane flight. I know the motion of the car caused me to fall asleep when a friend picked me up from Heathrow once. I would advise doing something that keeps you on your feet, active, and (weather permitting) in the open air. An informal neighborhood walk or a formal walking tour perhaps. You'll also want to eat again before checking in, but avoid alcohol until you've had a night's rest to recover from any jet lag.

Whatever you do, don't plan on doing very much. I've found that the best way to deal with jet lag is to go to bed early the first day, even if that means waking up early the next morning. Better that than starting out on a sleep deficit, and staying that way for the duration. The Hop On, Hop Of bus, or any other open ended activity is the right idea because you can go back to the hotel as soon as exhaustion sets in.

I have bought theatre tickets at 3--- I feel fine -- no jet lag and then slept through play

Thanks for all of the replies, sounds like a hop on bus is the right idea and then maybe a picnic in the park. My husband is trying to get tickets for Top Gear, so it may just be me and my son tooling about the first day. Matt- we are staying for the week in London...

I've flown to Japan across the Pacific Ocean from Seattle a half dozen times, and coming home usually land in Seattle around 9 in the morning. My routine is to go home, unpack, have some lunch, and then around 3pm take a 2 hour nap, sometimes less, sometimes a little more. I then wake up, have some dinner, go out for a walk, and then go to bed by 10pm and sleep well through the night. I plan to have a similar schedule when we arrive in Amsterdam at 8:30am from Seattle this September.