I'd say that one of the main issues refer to how the english schools structure their courses. They tend to concentrate their efforts on teaching the students the most correct grammar, as opposed to focus on teaching them how to use what they already know in simpler and more useful way. I mean, most of the students are looking for the fluency, which doesn't necessarily depends on how sophisticated your english is. If I were a teacher, I'd probably spend more time fostering my students to communicate among themselves and the grammar would represent a tool  and not the final objective of my classes.

For me, the main challenge consists in surpressing the threshold which exists between the native and the foreing speakers. 

Finding someone to practice with. As you probably know, almost nobody speaks English in Brazil. I learned English when I was eleven (now I'm fifteen), but besides English classes at school (which are very bad and teachers and students speak Portuguese to each other) I had no opportunities to speak it. Even though I watch videos and read books in English every day, I only speak English when I meet a foreigner, which doesn't happen too often. I wish I could speak more English, I find it a very beautiful language

Grammar and vocabulary weren't a problem, I find English easy because of its simplified grammar and it's very similar to Portuguese.