Getting around
You can get get just about anywhere via the tube (subway) or buses.
If you are going to be there for more than a couple of days, get a travelcard (aka an oyster card). this ends up being much cheaper than paying by the trip. You can pre-buy them in advance.
The train from Heathrow or Gatwick is cheaper and faster than a cab. the Heathrow express takes you to Paddington station and the Gatwick Express takes you to Victoria station. you will be able to get to anywhere in London from either of those 2 stations. You can also prepay for a shared van ($30-40 pp/each way). the van is a good deal if you have an early to mid morning flight back home.
if you don't know how to get somewhere, ask in the tube station and they'll tell you which line to which stop (and they can talk quickly so listen carefully).
Money
put your cards (credit and debit) into travel mode so the cards aren't declined because of an out of the country transaction.
use your ATM card to get money NOT the exchange bureaus. You will get the best rates from an ATM.
don't fall into the 1GBP = $1 trap. you'll go broke really quickly. 1GBP = $1.50 (as of 1/22/2015)
Buy a 100GBP (the AAA has the best rates for members) until you get there. The USD is supposed to gain value vs. the GBP over the next 12 months so you may not want to buy your GBP until last minute (a week or so ahead of time would be the latest).
Everything has VAT built into the price. If you buy anything expensive, see if they will do the VAT refund for you. That can add up to a big savings.
Eating
Food is much more expensive then you may be used to so don't be shocked
Sodas are not free refills.
Pubs can have decent food (or not)
British beer has a reputation for being "warm". It can be but its at the right temperature for the best taste.
Communication
If you have an unlocked GSM phone, you can buy a SIM card just about anywhere in London (carphone warehouses are all over the place). figure 10-15GBP for a pay as you go SIM loaded with 250+ UK min, 5000 texts and 500MB 3G. just make sure you are unlocked and GSM capable (my iPhone 5 from verizon is both). If you don't, you can pick up a cheap no frills 30 day phone for chump change.
Email your new phone number to folks back here and text it to your game buddies who are in London.
International calls can be added, usually 5GBP for 30 minutes or so.
Wifi is everywhere. Ask the server at your restaurant/pub, they will give you the password.
Skype is your friend. Put it on your tablet or smartphone.
Hotels
Hotel rooms in Europe are smaller than here in the USA and "superior" can really mean "just OK".Miscellaneous
If you smoke, bring your own. Cigarettes can be 10GBP ($15) per pack.
Take a picture of your passport and drivers license and email it to your free email account that you can access from any PC.
Ditto for your itinerary.
Beer comes in halfs and pints (go for the pints but be careful, their beer can put you on your a$$)
Being a Tourist
If this is a once in a lifetime trip, must sees are: The Tower of London and the Crown Jewels, the British Museum (mummies and the like), Trafalgar Square, Buckingham Palace and the changing of the Guard, the London Eye, Tower Bridge (not London Bridge, it just looks like a bridge), if the wife is with you Harrods (a department store like you have never seen) and Big Ben (it's the bell in the clock, not the clock itself).
Theater tickets: go to Leicester Square and you can get half price tickets at the cleverly titled half price ticket booth.