Having a clearly identified point of contact for course-related issues/concerns/questions. For example, my dissertation supervisor is someone who I work with, who is fine for asking questions specific to my dissertation. However, my course related questions get directed elsewhere, and it's important to be clear where this should be, and how the communication here should work.
Having an FAQ-style resource available for students detailing the types of support available, and when these would be available/applicable, is something that can work well. One thing that works quite well on our course is a separate discussion board area which is for questions that aren't specific to anything in particular where students can often get quick support for anything they need.
For an online-taught course, I wonder if any additional consideration needs to be given to identifying and signposting types of support available relating to health and wellbeing, as would be the case for students attending the university in person (e.g. access to student support services, chaplains etc.)