There's no easy answer! Democracy has brought forward many positive changes. In places where a city regards tourism as serious business, police work has been heightened drastically. It is unwise anywhere to leave valuables lying around or flaunt one's wealth, and the traveler generally does not venture far from the main stay (just as you would avoid certain parts of any other cosmopolitan cities). Brazil can now be regarded as no less "safe" than any region where wealth disparities exist. 

Just be discret: do not expose or carry expensive jewellery or photo/filming equipment.