Technical Writing course suggestions?

For me, what helped was doing a Master's Degree. And I'm sure a PhD would have continued to help. My advisors bikeshedded the hell out of every line I wrote in papers that had their names :). They also made me read specific material they had on how to write. But reading all those papers got me used to the model.

That said, it may not be the most effective method if all you want is the writing skill.

If your ok using a book, I would highly recommend the book The Pyramid Principle. It covers logical structure and logical thinking.

Practice.

Try writing a blog about something you know very well technically, but imagine you are explaining it to a Jr. Dev or maybe even a complete beginner.

Also, pay attention to the technical docs you like. For me, I think Digital Ocean does a really good job.

Experiment with drawings; simple sketches/models that can illucidate systems in a way that writing cannot.