If you want start an online course you must first know what others want. This is not what you want to teach others, but what they specifically want. You do this by building an email then asking. This is called a product launch. The first steps are to do a pre-launch. Once you have a large enough email list, start asking what they want. Then start giving it to them through 3 video presentations. Each video answers a different question and ends with the unanswered question for the next video. This sets you up as an expert. So, by the time you actually launch your product you will have a crowd waiting for it. That is if you have an email list. This crowd will grow over time, but you program your auto-responder email (e.g. Aweber) to go through the same series each time.

Best of Luck,
Mike
From the Trenches to the Towers Marketing
I will be willing to help as my time permits.
TheLittleGuysWayToRiches