Hi Arhur, bellow my recommendations:
1) EAT Mortadela´s Sandwich at Mercado Municipal;
2) DINNER at Terraço Italia with a 360 view of São Paulo (55 floor);
3) GO OUT at Vila Madalena´s Bars
4) For Italian dishes you can go at Bexiga
5) For Japones dishes you can eat at Liberdade neighborhood
6) If you come in January/February you can see the Escola de Samba (Samba school) training for the Carnaval;
7) walk thru between Historic center and see the Pateo do Collegio (Where São Paulo born), Largo São Francisco, Marco Zero and Sé church;
8) Watch the Classic soccer game like Palmeiras x São Paulo or Santos x Corinthias at Morumbi Stadium or Pacaembu Stadium;
9) São Paulo has around 1500 Pizza restaurant. Try any one and enjoy it.
10) If you like to buy clothes, go at Jardins Nighborhood, (there are a lot of good restaurants too)
11) Walk during the day at Ibirapuera´s Park and during the Night at Paulista Avenue;
São Paulo is a hub for several destinations in São Paulo. Try www.avianca.com.br and get low fares for a lot of Brazilian destinations.
I hope you enjoy your first visit in São Paulo, almost 7 years ago
Visit la Pinacoteca, nice building and galleries! (near Mercado Municipal). In Av Paulista, visit the MASP, an excellet museum. For a remerkable dinner, go to La Figueira Restaurant, in Jardins. It will be around 200 reais per person, but it will worth! about 6 years ago