Heading over to Old Blighty for a few days of vacation? Make sure you're prepared, so that once you've gotten here, you can take in the sights and experiences instead of scrambling to get the necessities in order.
Do a lot of research about London and what it has to offer before heading in this direction. Knowing what's available will help you narrow down your choices of what to see and do. Try a travel book on the city itself, like Frommer's "Irreverent Guide to London."
Make a list of the things you want to accomplish on your trip. Narrowing it down to one or two activities per day is the most rational way to go. This will help you determine how many days you should plan to be in London.
Create your London itinerary, allowing time for travel, a day for jet lag recovery, and some flexibility in case you stumble onto something unexpected along the way.
If you're staying in London for five days or more, purchase an Oyster card at your airport's Tube terminal. You'll want to buy a week pass for zones 1 and 2 so you can move around easily and frequently without needing to add more money. This will set you back about £25 and give you access to all of the buses and subways in the city.
Grab a Tube map as soon as you enter your first Tube station, and if possible purchase an "A-Z Guide to London," which will help you out if you become lost in the city. It is the essential map of greater London, and even locals own one.
Try to book at least the first night's accommodation in advance, and make sure it's near a Tube station so luggage transport is reasonably easy. English hotels might be different than those you're used to in the States, so book only a night or two, just in case the accommodations aren't up to your standards.
If you plan to go outside London, perhaps to Stonehenge or Oxford, be sure to budget that into your travel expenses. You can rent a car, take a train or use the tourist buses that will take you from Central London to your destination.