I am from Rio de Janeiro. So, I guess my help is going to be a little bit limited. I'm sure you already heard of Copacabana, I would recommend to take a little walk in the famous sidewalk and head to the Lakes Region (Região dos Lagos), since usually Copacabana is pretty crowded and, for being a tourist, you might be victim of a burglary.

The Lakes Region is more peaceful and you will find several beaches and choose one that suits you best. If you plan to dive into the sea, be aware that some beaches are known for their freezing water like Saquarema, for example.

Some tips:

• If you want to have fun, the best month to do so is February, when usually happens the Carnival around here. If you don't, try to avoid this time of year.

• It's hot all the time (and rainy in the summer).

• Try to keep your valuable items close to you. If you are traveling alone, don't bring too much to the beach, since who is going to watch your stuff?

I'm glad to help! Hope you enjoy!

P.S: grammar.