I have a lot of Brazilian students at work, these are the most common issues I see - not sure if they'll apply to you though.
We don't use 'know' to mean having traveled to a place. Many students say, "Have you know Brazil?" when they should say, "Have you been to Brazil?" or "Have you traveled to Brazil?"
We use 'be' to indicate years of age, not 'have'. Many students say, "I have 26 years old." when they should say, "I am 26 years old."
Lastly, there's often some confusion on the differences between 'speak' 'say' 'ask' and 'tell'.
Final t's and ti's often turn into 'ch'. So they call Cincinnati /sin-sin-na-chee/ instead of /sin-sin-na-tee/.
Pronunciation of the hard English R and differentiation between 'r' and 'h' comes up a lot too.
Of course different people have different things they have troubles with, but these are a few I find common in Portuguese speaking students. Hope it helps!