Be carefull with the "Marginais Pinheiro and Tiete" Avenues. Next to 9:00 am and 18:00 its impossible to drive there. Try to avoid these times. And pay attention when return to the airports (Congonhas and Guarulhos) because you have to take the avenue...
Traffic is a real b**** here, so allow plenty of time for your trip whether you're taking the bus, taxi, subway or car. Things get worse when it rains and/or during rush hours.
Coach travel: I was on a coach and it took us one hour just to go from Tiete Bus Terminal to Dutra highway exit. A simple one-hour and half trip took almost 3 hours! Luckily we were prepared and had food and water with us, and no commitment in our destination.
Subway: We were at Liberdade station and had to wait 4 times to manage to get inside a wagon because it was so crowded! A little tip, the first wagons are usually less crowded.
Real-time traffic information (in Portuguese)
When you shall go by bus from Sao Paulo, check what bus station your bus leaves from. They have three big bus stations here, so it can be a problem for you if you dont check up from which one you shall take your bus. Good luck with your trip and dont go to the wrong one.
Obviously there is alot of it, 4th biggest city in the world, be wary of trucks and buses as lanes are very narrow. Cabs are ample and are solid.
At night, most drivers do not obey red lights, as it is perceived to be dangerous to stop late at night, so honk or flash lights.