I think something very useful would be to find out about their likes and preferences, hobbies, that sort of thing, in the first place. You can then use this information to plan your class activities and your students are likely to be more motivated than discussing, say, Wuthering Heights, if it isn't the sort of thing they're attracted to. (W.H. is a silly example; I exaggerated on purpose.) Even grammar examples will be more easily retained if they deal with stuff your students are conversant with.
Perhaps I'm stating the obvious. I'm not a teacher; I have been a student and have had enough of tedious topics I didn't care for at all.
- For Teachers