As preposições AT, IN, ON causam muita confusão entre os Brasileiros.

Então vamos ver o uso dessas preposições quando precisar dizer (no, na, nos, nas, em, às):

AT 

1. for places in general (e.g. I work at …; I stayed at home; I’m at the bus stop) but, I go towork by bus
2. telling time (e.g. I start work at 08:00; I have dinner at 09:00pm) but, “what time is it?” “it’s5:00″
3. full address (e.g. I live at 885 Rui Barbosa Av.)

IN

1. inside (e.g. I’m in my house now; the CD is in the box; we’re in the class)
2. neighbourhood (e.g. I live in Santa Felicidade)
3. city (e.g. I live in Santos) but, I go to Santos every month
4. country (e.g. I live in Brazil) but, I’m from Brazil; I’m going to France next month
5. only year (e.g. I was born in 1971)
6. only month (e.g. I was born in July) but, I was born on July 13th

ON

1. touching the surface (e.g. the book is on the table; the picture is on the wall)
2. inside public transportation (e.g. I’m on a bus; You can’t use your mobile phone on a plane)
3. days of week (e.g. I study English only on Fridays; the meeting is on Tuesday)
4. only street name (e.g. I live on Rui Barbosa Av.)
5. days (e.g. I was born on the 13th)
6. dates (e.g. I was born on the 13th of July 1971; the company was founded on May 01st)