Hi Mario! Sorry it took so long to write back!
Ok, so you're visiting Sao Paulo! That's awesome! It's a huge city, but the coolest thing about it is that SP is not touristic at all... you'll be able to see people living their real day by day life.
The best sites: Av. Paulista, a very busy and beautiful avenue, with lots of museums, galleries, bookstores and nightlife (specially at Rua Augusta); Vila Madalena, our alternative neighborhood, with different shops and art galleries, and with an amazing nightlife (mainly bars and restaurants). For nightclubs you shoul head Vila Olimpia. Just go there and you'll find an option every corner.
Good sites to visit too are the Ibirapuera Park specially on the weekends, when there's a lot going on; the Ipiranga Museum (Museu da Independencia) if you like history, and the central area of the city, specially around Anhangabau (the oldest part of the city, with beautiful architecture - and tons of people).
About safety: the most important thing is to be aware all the time, and don't show your expensive things (cameras, cellphones and MP3's). Make sure to keep your eyes on your stuff all the time, specially in the central area of the city... usually pickpocketing is the most common thing to happen. And at night avoid dark areas, stay where the people is, and you'l be fine, ok?
I'd show you around if I was in SP, but now I'm in the USA with my boyfriend... so good luck and let me know if you need any other information, ok!?