Just wanted to recommend this new(ish) course on teaching English online - https://www.futurelearn.com/courses/online-tutoring. As with all teaching courses, if you have some experience then parts of it will be telling you things you already know. But even with some experience of teaching online I found it really useful. You can take it for free, or it's a pretty reasonable £42 to obtain the certificate and have permanent access to all the resources (disclaimer: I don't work for them and nor am I referring!). Hope that's of interest!