As a teacher (of adult students, by the way), what I would wish from my students is a curious mind and a willingness to try something different. Also, the guts to speak up makes a world of difference.
The times I find difficult include when the students sit and expect me to simply hand them English as if it were some physical object. Language is about communication and engagement, so I need some input from them (even if it's the most broken form of English) to really move anywhere.
Really, I'm very happy to throw out a carefully-planned lesson if the students are interested in pulling apart and playing with another point of grammar, talking about a different topic, or dealing with any other part of English. Bring something to the table as well.
I find the students who aim to be "perfectly correct" also struggle on other levels. If they can complete a written exercise perfectly and quickly at intermediate level, but can't respond to a question such as "So how was your weekend?", then there's a problem. Please, say something. Invent something if you can't think of anything. Say anything, just open your mouth, dammit.
Some students who I teach at upper-level don't want to say anything. I also have beginner students who struggle with sentences, but who also joke, laugh and want more words and phrases to play with. Guess which group I prefer teaching? ;)