In the past I have included the following statement on my syllabus:
Office Hours: Mon 1-2pm, Weds 3-5pm, or by appointment
However, I am beginning to get too many requests for appointments. Appointments are really inefficient. They waste both of our time trying to schedule them, and with multiple appointments per week in addition to office hours, even holding them takes a lot of time away from research. How do you accommodate students who can't make your office hours without devoting too much time to this task?
I thought about setting up a class message board where they can ask each other and answer each other's questions - anonymously if they wish - (I can also answer questions on the message board) and put on the syllabus "All content related questions should be posed in class, on the message board or in office hours. I do not reply to questions about content via email. Please schedule an appointment to meet with me if you are having difficulty getting a question answered after trying the above options"
Some Background: I'm a graduate student lecturer. I teach 2 sections of calculus, so about 60 students. Since classes are small (~30), there are about 10 lecturers (some are faculty and some are grad students with masters degrees) and we all have office hours. Mine tend to be very crowded, about 5-10 students showing up (some from other sections). I tell my students to go to other instructor's office hours, but they say they aren't as helpful.