I think that profs should really give extra emphasis to the fact that they are available to the students, and then follow up on that by actually being there when they say they will be. I find that one must be particularly assertive in this regard with first year students. You will be surprised how effective a note on a returned paper, speaking to a student privately once in the hall or library, or the such will be in encouraging a marginal student to really start to take interest in the course. After the first test was in he wrote personal notes to all students getting below some grade, saying that he wanted them to do well, and he had confidence they could, if they only came in for some help. I forget the numerical details, but the results were astounding.
Little things can make a big difference.
Don't just say you are available once at the beginning of the term, repeat it regularly through the term. Leaving your office door open can make a huge difference. Be sure that tests, assignments, etc. are fair, valid, consistent and explicitly described . Nothing can more readily sour a teaching relationship than something which is seen as being unfair. And finally, several students suggested that professors too seldom seek meaningful feedback .