Take train. The express train, Heathrow Express, is the quickest way into central London, which takes about 15-20 minutes. The regular train, Heathrow Connect, also operates between Heathrow airport terminals 1,2 and 3 and Paddington subway station in London. The regular train takes about 25 minutes. Passengers travelling at terminal 5 should use the free inter-terminal service.
Or Take subway (called Tube in London). The Piccadilly Line connects all Heathrow terminals with frequent services to London.