By Road:

Although the majority of journeys involving Central London are made by public transport, car travel is common in the suburbs.

The inner ring road (around central London), the North and South Circular roads (in the suburbs), and the outer orbital motorway (the M25, outside the built-up area) encircle the city and are intersected by a number of busy radial routes—but very few motorways penetrate into inner London. The M25 is the longest ring-road motorway in the world at measuring 195.5 km.

By Bus:

London's bus network is one of the largest in the world, running 24 hours a day, with 8,000 buses, 700 bus routes, and over 6 million passenger journeys made every weekday. In 2003, the network's ridership was estimated at over 1.5 billion passenger trips per annum, more than the Underground. 

Around £850 million is taken in revenue each year. London has the largest wheelchair accessible network in the world and, from the 3rd quarter of 2007, became more accessible to hearing and visually impaired passengers as audio-visual announcements were introduced. The distinctive red double-decker buses are internationally recognised, and are a trademark of the London transport system.

By Air:

Heathrow is the UK's main airport and is London’s largest. Located on the western outskirts of the city, Heathrow is also one of Europe’s leading international hubs. Around 63 million passengers from all over the world travel through Heathrow’s four (soon to be five) terminals every year. 

Heathrow is only 15 miles outside the centre of London and is well connected with the public transport system. You can take the Heathrow Express train to/from Paddington Station in the centre of London.