Knowing just how high we can realistically set our expectations requires knowing our students. Experience helps here, and so does data gathering. We have two different kinds of opportunities. First, we can communicate expectations by what we ask of them. Second, when we provide feedback to students, we can honestly let them know what they have done well and where we think they can achieve more.
Good practice respects diverse talents and ways of learning.
Students differ along many important dimensions. Each brings a distinct set of strengths and challenges to the role of students. The simplistic, and pragmatically unrealistic, response to this observation is to try to match teaching styles with learning styles. What we can do is try to make our teaching as complex as our students are. Metaphorically, I think this principle calls for buffet teaching instead of fixed menus.