1. I always buy an Oyster card, which you can use on the tube (subway), buses, and some suburban trains. You pay a 5 pound deposit, then load it up with money to pay for transportation. When you leave, you can get any remaining money back, including the 5 pound deposit. There are also day passes or 10-ride passes, but I've generally found that the Oyster card works best for me.

2. I don't really understand this one — I've never had any trouble with train routes, mostly the whole thing is pretty intuitive. It can get complicated if you are trying to get to a small suburban station that some trains stop at and others don't, but that's about the only exception.

3. In central London, the must-sees are Westminster Abbey, the Houses of Parliament/Big Ben (right next door to the abbey), the British Museum, the Tower of London, Trafalgar Square, Buckingham Palace (sign up way ahead of time to visit the interior) and maybe St Paul's cathedral. I would also consider going to a play or musical in the Leicester Square area to be a must-see or must-do in London. The next tier, almost must-sees but slightly less than the previous list, includes Kensington Palace, the Victoria & Albert museum, the Tower Bridge, Greenwich (a bit further out, not really in central London), and, if you like paintings, the National Gallery. The London Eye, National Portrait Gallery, Harrod's, Kensington Park or Hyde Park, St James Park, and the Royal Mews are in the next tier. I'm sure I missed some, but this is the main stuff.

However, there are some must-sees that are outside central London, notably Windsor Castle. I would put it in the highest tier of must-sees. Either Oxford or Cambridge are also on my must-see list, although each is a full day-trip from London and could be seen as part of a general tour of England. I favor Cambridge (it's a prettier town), if you have to choose between the two, but both are awesome. Hampton Court Palace is also awesome and a must-see-type place, albeit less so than Windsor Castle and one of Oxford/Cambridge.

Other great daytrips that can be done easily from London include Stonehenge, Salisbury, Winchester, Leeds Castle, Canterbury, Stratford-upon-Avon, Dover, and Bath, roughly in that order of priority. Some of these can be combined in one daytrip, such as Stonehenge/Salisbury.

4. Heathrow sucks, but you should be fine getting there 2 hours ahead, or maybe 2 1/2. Be careful to know which terminal, however, as some of them are far apart and it isn't so easy to move between them quickly. I stayed at a hotel in Terminal 4 last weekend and had to take a 10-minute cab ride to get to Terminal 3 — would have taken 25 minutes if I tried to get there on the train, I was told.

5. I got pickpocketed just outside the Tower Hill tube station. Be careful around there, and around most other crowded tube stations in touristy areas. They seem to target people carrying luggage or big bags or kids, who are distracted.