The best way to navigate around London is by public transport.
It is so much cheaper to buy an Oyster card then daily paper tickets.

Note that you will need an Oyster card or paper day travel card to travel on most central London buses as you cannot buy tickets on the bus (there are ticket machines at bus stops, but these are often broken).
Oyster cards are available from all London Underground station ticket offices. We suggest you buy an Oyster card as soon as you arrive.

The cards require a £3 refundable deposit and then it is up to you how much credit you put on the card. Daily unlimited use of the card within Zones 1 – 2 is £5.10. If you are staying longer than one week, we suggest you get a weekly card at £25.80 for unlimited use of public transport for one week.

For further information on travel visit:

Transport for London:

http://www.tfl.gov.uk
http://www.tfl.gov.uk/faresandtickets
http://www.tfl.gov.uk/tickets/oysteronline/2732.aspx

Info on Visitor tickets: there are special visitor Oyster cards available. The deposit for the card is £2 and any money left over on the card below £5 is immediately refunded to you when you return the card to a ticket office. Amounts above £5 need you to fill a form.
http://www.tfl.gov.uk/tickets/faresandtickets/visitortickets/5185.aspx
note: these are not able to issue 7 day bundles. If you are staying a week or more, the cheapest option is to take a weekly ticket available only on standard Oyster cards.

National Rail:

http://www.nationalrail.co.uk

Taxis:

it is easy to hail down one of London's iconic black cabs from any street corner. Alternatively, if you would like to book a taxi, we can give you the telephone number of a mini-cab service or even book one for you.