Advices for Sao Paolo (São Paulo)

Hi,
I am planning to travel to Brazil in May on my own. I will proabably do Sao Paolo, Salvador and Morro de Sao Paolo.
I feel quite confident with Salvador and Morro de Sao Paolo (even though advices for these places are welcome too) but I feel a bit lost when it comes to Sao Paolo. Could anyone advice the best area to live? As I am travelling on my own I want to stay in a fairly "safe" area. Any other important things I should be aware of?
Thanks a lot in advance!
Pernilla