Brazil requires honest safety preparation. São Paulo and Rio have serious urban crime, and tourist areas are not immune. Do not walk with your phone visible; do not wear jewelry or expensive watches; use official taxis or Uber rather than hailing random cabs. In Rio, research which favelas offer organized tours (safe and valuable) versus those that don't.
Away from major cities, Brazil is often much safer — the Amazon, Pantanal, and interior states see far less crime. Health considerations: yellow fever vaccination is required for many national parks and the Amazon region — get this well before departure. Dengue fever is present; use insect repellent. Tap water quality varies — stick to bottled water outside major cities.