Providing timely and consructive feed back is essential not only in person, but online as well.  It is important to phrase you feedback properly to enhance learning if it has to be corrective.

An online presence needs to be human as well.  When a student knows about you as a person, they view you as more than just a talking head on the screen that can be ignored.

Being an online instructor is more than just being able to regurgitate information.  You have to be able to take the classroom experience and bring it to life on the computer.  The student needs to know that they can ask you questions offline as well as online.  You also need to be able to explain not just the xontent but how to utilize the technology as well.