Tips for visiting Rio and weather conditions in December/January?

It will be very hot, with temperatures peaks higher than 40ºC in the afternoon. During the night the high temperatures and humidity makes it very unpleasant to sleep without an air conditioner. I advise you to make *SURE* your place have one. 

In december is going to be very hot, very very hot and lots of tourists

Try Jardim Botanico as well or Parque Lage

Go with the bondinio in Santa Teresa have acai there and then you can go to Selaron Steps. 

For the night life Lapa is the best but as well the bars in Botafogo

I don't know if you like trekking but you can try Dois Irmaos - is not difficult and is only 45 minutes (but you have to go to Vidigal - which is a favela and take a mototaxi or a van that will let you at the beginning of the path but try not to go alone - i mean I am a foreigner and i went there with a friend of mine (foreigner as well) and we met others foreigners who were going so it was ok but even if it's a pacified favela you have to take care

It'll be hot and very humid. It'll be smack in the middle of the summer. Don't be fooled by temperature readings. For some reason the heat feels worse than it looks on a thermometer. 

Dress for Rio. Don't wear expensive, heavily branded or otherwise flashy clothes. Leave unnecessary accessories/jewelry at home unless it's obviously cheap. Go local and wear flip-flops, but do yourself a favor and buy them in Rio. There's nothing like a pair of Havaianas and they're cheaper in Brazil than they are in the UK. 

Take precaution with your personal belongings on the beaches. Things get stolen from unsuspecting tourists all of the time. Don't leave your items unattended anywhere at any time.

Only carry the cash that you need and don't flash it around. Just be discrete. The same goes for phones and expensive cameras. 

Don't walk around at night, especially alone and ESPECIALLY if you've been drinking. 

Stay out of the favelas. Even for the tours. No one likes poverty gawkers. 

Ipanema and Leblon are among the nicest and safer neighborhoods to stay in Rio. The location is better for getting around. Personally I like Ipanema best. Copacabana is kind of meh and crime is spiking there a bit these days.  

Use cabs, don't bother renting a car unless you want to spend a massive portion of your vacation sitting in traffic. Chances are you're not prepared for driving there anyway. 

Don't swim at the beaches in Rio. They're beautiful, but believe me, they're heavily polluted. If you want to swim at some beautiful beaches, take the two hour trip to Cabo Frio. 

Use sunscreen and mosquito spray liberally. Dengue is a problem up there right now. 

Take the train up to Christ the Redeemer. The ride is half of the experience. 

Sugar Loaf is best for sunset. 

The botanical garden is a really lovely way to spend an afternoon. 

Santa Teresa is a beautiful neighborhood that's worth checking out. It's old Rio and it has some really great restaurants. Namely Espírito Santa for dinner and Cafecito for a late breakfast or lunch. 

If you have the extra time and want to see a little more of Brazil. I highly, highly recommend driving down to Paraty. Any other or more specific questions you may have, I'd be happy to help with. Have a safe trip and great time here in Brazil! 

Rainy weather, Best Time to visit Brazil is from June to November in my Opinion.

It is HOT LIKE HELL, if you like heat and sun then go for it! Don't forget to bring your sunblockers! 

Hi Philip, if you wanna know more than the most usual places, I recommend that you go to smaller cities with beautiful beaches.

For example, have you ever went to Arraial do Cabo? There you can find a lot of beaches, including "Praia do Forno" (in my opinion, the most beautiful in all State). Other cities you can visit: Cabo Frio, Búzios, Niteroi (in the same region than Arraial) and Parati.

If you have any other question, let me know!

Have a good trip