We have found that the traditional method of setting aside blocks of time for students to drop in for questions or discussion has not worked well. Instead, you might consider telling students that you can be available before or after class or on an as-needed basis, by appointment.
Many instructors have successfully used the Brown and Brew coffee shop in Curtis Hall, the Commons or Hotung Café in the Campus Center, and the Tower Café in Tisch Library for student meetings. In fact, to encourage your interaction with students, if a student joins you at the Tower Café, you can both get free coffee by simply telling the cashier that you are faculty.
If you prefer a more private space, however, contact our office in advance, and we can reserve a room for you.