Where to learn about topic creation? I've been a copywriter for some time now, but have never been given autonomy over what topics to cover.

I would like to expand my services into SEO keyword research and topic creation. Keyword research is very much easy to find resources on and to practice, but I'd like to know how to marry it with content startegy/topic creation. 

Are there some online courses on this? Or am I overestimating how much there is to it?