Here's my suggestions:
- Spend at least one day on the beach at Ipanema. Choose a kiosk, rent some chairs and umbrella, bring a book, and have them bring you cold beers, coconuts and caprinhas all day as you watch the parade of people and bikinis. The water is clean in Ipanema and waves can be pretty big too. Once it cools down, take a long walk along the promenade to Copacabana.
- Do Copacabana at dusk/early evening. Grab a beer and some live music at one of the kiosks on the promenade. It's always buzzing. On Sunday, they close the traffic as well, and will probably have various events for the World Cup.
- Rio has a rent-a-bike system, although I found it impossible to use as a tourist. There's a lady who rents bikes on the corner of Miguel Lemos and Avenue de Copacabana for R$10 an hour.
- Visit the Botanical Gardens, which are quite lovely.
- Definitely eat in at least one churrascaria. The most famous is Porcao. It's about $50 a person, but it's an experience. Here's Time Outs round-up of the best churrascaria's in Rio.
- Take a favela tour of Rocinha. It's a fascinating (and safe) glimpse into a very real and vibrant part of what makes Rio tick.
- There's a souvenir market in Copacabana (on the corner of Miguel Lemos) each night, and a day market in Ipanema on Sundays.
- Drink some of that freshly squeezed fruit juice! Try fruits you don't have at home, like caju, acerola, camu camu, and jabuticaba. Skip a meal and try a bowl of sweet, thick acai.
- Visiting Sugarloaf Mountain and Christ the Redeemer are the two most popular tourist traps (for good reason). If you do one, do Sugarloaf which is easier to get to, and has better views of the city. If you're splurging, a helicopter ride over Rio on the clear sunny day is incredible.
- Ask around if there are any live samba shows. The music and atmosphere are amazing.
- Lapa is is the late-night party district. Some people love it, others find it a little seedy.
- Samba schools have rehearsals which are like massive hall parties. Worth checking out if there's one happening nearby.
- Go hang-gliding over the beach, which is unforgettable in all the right ways.
Here are some cool insider tips of other suggestions to keep you busy: 10 Best Things to Do in Rio
Definitely take your common sense with you. Don't carry too much unnecessary cash (just about everywhere takes credit card, leave a back-up at the hotel). Make sure the taxis look official (have phone numbers, licenses). If someone puts peanuts on your table, don't eat them unless you want to buy them (If you leave them, they'll just take them away). Don't stray too far from well-lit, busy areas at night. Traffic can be intense so try not to be in a rush to get anywhere, and give yourself plenty of time to get where you're going.
Besides being one of the most beautiful cities in the world, Rio has an energy all its own. Whether you're there for Carnival, the World Cup, Olympics, New Years, or any other time of year - you can't really go wrong.