Herberth, to make payments easier for clients I recommend that you to incorporate in the US. Being incorporated in the US usually also clients more confident since you're now liable in the United States. Talk to a good Brazilian accountant and he or she will help you with local legal issues (handling the Receita Federal).
This make a lot easier negotiating with clients. People often feel more safe when they do not have to transfer money overseas, especially when doing freelance work to small companies or individuals.
I personally find this difficult. Average Brazilian salaries are not really that far from international salaries and usually will be near average salaries in lower paying European countries like Spain or Portugual. Outsourcing to Eastern Europe or India is way cheaper than Brazil, especially when you take in account the amount of taxes we pay here (and the Banco Central transaction costs to take money back home). Living in a lot of Brazilian cities like Rio or São Paulo is also very high, often on par with international cities, if you want to live a middle class life style.
I've done a few odd jobs finding posts on craigslist, you might give it a try, too. For me it was more important having experience handling international contacts and having a chance to try my English in real world.
And, by the way, good luck :)