The importance of learning Portuguese when (or better before) coming to Brazil cannot be stressed enough. Jobs that do not require Portuguese are extremely rare and as being a job hunting foreigner in Brazil is hard enough, you want to make sure that you can apply at least for all jobs you qualify for.
The other top priority is proper networking. In Brazil, it is often not what you know, but WHO you know that gets you a job. Start with social activities like joining a sports club where you can meet new people in an easy-going atmosphere. It goes unsaid that the better your Portuguese skills are, the easier it is to make new contacts. Later you should contact companies which are directly in your field of interest.
In order to save yourself a lot of trouble and an extremely tough time during your first few months in Brazil, get a job prior to your departure! As a work visa is very hard to obtain, and is only issued in certain cases (see visa section), you should apply for it before leaving for Brazil. Yet in order to do that, you will need a pre-arranged job. You will also need your employer to start the application process for your work permit.
Where to look for a job
Apart from networking you can also look for jobs in newspapers, agencies and on the internet. One of the most popular sites for job searching is Catho.
You could also search the websites of large multinational corporations or inter-governmental agencies that are based in Brazil, if you have the correct qualifications. Your home country's chambers of commerce and embassies also provide job offers or a list of international companies based in Brazil.
When looking for a job be cautious of fraudulents. Many agencies and headhunters take advantage of the problematic job situation for foreigners and provide very tempting job offers which eventually turn out to be false. Do not pay money for any services as this is always a sure sign of fraud!