Brazil is not only a simple tourist destination but a place where all soccer fans gather, especially with upcoming FIFA World Cup that is set in the country so the whole nation is currently very busy with preparing for the event and also for the massive number of foreigners that are going to enter the country. For foreigners, they know that Brazilians are generally friendly but they should not take advantage of this trait and learn to understand the local customs. This is also to avoid you of embarrassment.
Avoid getting impatient while you stay in Brazil. If you are a time conscious person, you will find it tough being in the country. Lateness is considered normal here and a part of their lifestyle. You will notice how the locals behave when they are rarely be on time on almost anything such as the long queues at supermarket counters or ATMs. Most things move really slowly here than you used to be so if possible ignore the lateness and learn to mimic how the locals behave, at least temporarily for the duration of your stay in Brazil. Also when you hear a Brazilian saying 'estou chegando' which literally means 'I'm arriving' it can oftentimes mean that they are just about to get ready to leave from their home and will arrive soon.
Most of the South American nations speak Spanish but Brazil speaks differently and almost identical to Spanish which is Portuguese and other 2 languages. Most of the locals can speak a little English and will be glad to get the opportunity to practice speaking them but on your part if you have not mastered the local language, it is best to stick with talking in English and do not speak Spanish. The locals will highly appreciate your effort for speaking in Portuguese if you know basic phrases in communicating with the locals and they will never mock you when you attempt to talk in the local language.
Since you will be visiting the country for the FIFA World Cup, be careful who you root for. Although they do not mind you rooting for your own team as long as your team is not against Brazil and also assuming that your allegiances do not fall with Argentina. There is a fierce rivalry going on between these 2 countries so you should be extra careful in your way of expressing admiration for other teams, especially when they are one of the rivals of the country.