Anyway, I've been lucky enough to spend a fair amount of time there thanks to an internship in college and subsequent visits, and I know the city fairly well. Since I am often asked for travel tips, I decided to transform my usual cut/paste email into a post that I can distribute instead. If any of you have other tips or recommendations, please leave a comment!
[Disclaimer: I'm familiar with London, but not an expert, and I do not live there. I'm sharing what has worked for me, and how I save money and time, but you might totally hate it.]
image by me (as are all of these, unless otherwise noted)
Getting Around
If you're flying from the US, you'll likely end up at either London Heathrow or Gatwick airports. Both are pretty far from the city center, and unless you've booked in advance for a large group, a taxi is not an economical option. Seriously, it's about $150 USD for a cab from central London to Heathrow.
However, the Underground runs all the way out to Heathrow, and you can buy day passes at the terminal and ride all the way to the city center in about an hour, but isn't a great idea if you've got lots of luggage. You can also take the Heathrow Express train to Paddington Station in about 15 minutes, and then transfer from there via Underground or taxi.
You'll probably find the Underground (aka the tube) and bus system easy to use once you take a moment to sit down and study the map. The Transport for London site has several online tools and maps that you can download, including bus routes that take you to major sites. To avoid confusion, I recommend buying a multi-day pass (for Zone 1) and paying the small deposit for the plastic card that you scan in/out of stations and on buses. It's much simpler than keeping single fares on hand, and you can get your deposit back at any station before you go. I buy mine at the Heathrow terminal before heading downstairs to the trains.
Only take the official black cabs if you are hailing one on the street. Unmarked "minicabs" can rip you off, unless you book them in advance through a reputable company. I use a service called UniCab to book taxis, and they have an app for your phone/tablet. You can put in your start/end destination and then reserve a cab and pay in advance online. It's safe and the car companies are legit. This will be cheaper than hailing black cabs, but you need a mobile phone number to confirm everything if you're booking online.
Where to Stay
You will not hurt for choice in London, and you can rent hotel rooms or flats for a huge range of prices. However, it's worth paying for a central location. I recommend a place near a Central line station (the red line on the tube map) because it has connections to pretty much every line you would need and makes coming home at night quicker.
Before you book anything, use Google Maps to see how long it will take you to walk to the nearest Underground station and bus stop. You may be doing this in the rain, and with sore feet.
Here are my thoughts on the main sites in the city (in no particular order):
