The fastest and best way to improve your language skills is by doing a lot of self-study and also paying a professional teacher to help you with questions, correct your mistakes, and give you new grammar, vocabulary, writing help, and other special things like business skills if you need English for your job. These skills might be meetings and presentations in English, telephoning and e-mails in English, etc. As part of your self-study, you can use italki to find native English speakers who want to learn Portuguese (this is called a “language exchange”) or community tutors who will help you with English. Mostly, you should put as much English as possible into your head: listen to podcasts, watch TV shows and movies, and read things in English. If possible, watch TV with English subtitles so you can read and hear the words at the same time (do NOT watch with Portuguese subtitles!). An excellent English learning web site is http://www.elllo.org — they have hundreds of short dialogs between two people from different countries speaking English. You can read the words as they speak, and it will give you good practice understanding different accents, as well as learning vocabulary. If you want to study for an exam, you really should find someone with experience to help you: of course, you will probably have to pay that person, but this is a serious thing and you don’t want to fail the exam. Good luck!