Online Learning Consortium promotes their Online Teaching Certificate which covers a wide verity of topics. However, here is their brief overview of the basic skills instructors usually wonder about if they have not taught online:

• Educational Technology: While the basics of email, discussion boards, and PowerPoint are necessary, you’ll also want to learn to use meeting software as well as have an understanding of learning management systems. Additionally, it can’t hurt to have a base understanding of how to troubleshoot computer issues, internet connectivity hiccups, and incidents of malware to keep your systems running smoothly.
• Time Commitment: Think online teaching will take less time than teaching face-to-face? Not necessarily. You’ll find that more time is spent one-on-one with students via email and chat rooms, especially with asynchronous programs. And since many online courses are open to students across the globe, you may need to consider the time differences when scheduling synchronous sessions.
• Student Engagement: Unless you are working in a blended learning environment, you may never meet students face-to-face. If that’s the case, take the time to cultivate an online presence so students and colleagues can get to know you. Also, plan to spend time responding to emails and discussion board posts.  Most institutions have policies surrounding faculty-student communication requirements.