I have been to London a few times and it's very expensive. Here are a few things I learned. Pickup a copy of London A to Z you will need it to get around. Also get a copy of
TNT magazine great for place to stay, clubs, jobs and travel. I think there is a nother similar one but I don't remeber the name. For finding out how to get by cheaply stay in a hostel for a week or two, many people stay in them for a long time and can give you great advice for getting by for not much. Their are many hostels by the Earls Court tube stop, also has a Tesco near by. I also stayed in Camden Town nice if your a drug addict, but it was cheap, their is a big outdoor market here. Hope this helps.
One last thing you need to do is find a Kiwi and ask them to take you to Church. I don't remeber the location but for 5 pounds you could drink all the beer you wanted out of plastic bags. This is a must see.