A big city needs a big airport, and São Paulo has one in the Aeroporto Internacional de São Paulo/Guarulhos–Governador André Franco Montoro (Guarulhos for short, or Cumbica locally). It's Latin America's busiest airport, so you won't have a problem finding flights: there are regular services from London Heathrow and Paris Charles de Gaulle as well as a host of major US cities. If you're heading off to Rio or elsewhere in Brazil, you might take off from the nearby Aeroporto Congonhas.
Trains
The grand Luz station is the place to arrive by train; it's also a subway station.
Automobiles
Early morning and late afternoon traffic jams bringing the city to a standstill are notorious here – get into a car at your peril.