Always this. Just write. Find a sample unit of your target audience, and ask them to read your posts and give you feedback (what was hard to follow, boring, int

Always this. Just write. Find a sample unit of your target audience, and ask them to read your posts and give you feedback (what was hard to follow, boring, interesting, too much background, too little, etc) and iterate. As for #2, if you have a friendly prof for a relevant course or two, ask them directly! Chances are, they'll be happy to have you write about what you learned from their class, and may even be willing to read your posts and give you feedback.