One of the most difficult things about learning English is mastering the correct pronunciation of words. To be clear, I am not talking about losing your accent, which, depending on how old you are when you learn a new language, may not even be possible. What is possible, however, is to correctly pronounce words, even if you do pronounce them with an accent. Here are some tips to help you improve your pronunciation in English:
Speak slowly and exaggerate
Sometimes when I try to speak Portuguese fast (so as to sound like a native speaker) I end up mispronouncing many words, which definitely does not make me sound like a native speaker! To avoid this make sure you speak slowly and exaggerate the different sounds i words. You may feel a little silly doing this but it will help avoid slurring your speech and help you build good habits.
Watch out for difficult sounds
There are some sounds in English that are more difficult to pronounce than others. Pay special attention to the sounds that give you a hard time and practice them. Two sounds that are very difficult for non-native English speakers are the "th" sound and the hard R sound. Try to master these two sounds as it will help you sound more like a native speaker. One tip to help with the hard R sound is to imagine speaking in a caipira accent (think of how someone from the interior of São Paulo would pronounce the R sound in porta or carne).
Pay attention when listening
There are sounds in English that don't exist in Portuguese and vice-versa, as such there are sounds that will require you to use your mouth, tongue and throat in ways that may be unfamiliar. For this reason it is important to pay close attention to native speakers when they're speaking, watch their mouths and try and imitate the same movements.
While you may feel a little silly recording yourself speaking, it is a great way to improve your pronunciation. Compare your pronunciation with that of natives. See which words you pronounce the same way and which words you need to improve upon.
Google can be a great tool to help with pronunciation. If you're unsure how to pronounce a word just google,"pronunciation (the word you're trying to pronounce)". Google will give you a phonetic spelling of the word along with an audio of the word being pronounced. The audio can be slowed down to help break down the different sounds and you can even choose between American and British pronunciation.