ksarn.org
… with a specific prompt and a clear expectation for engagement, for example one original post and two substantive replies by set dates. Build that structure in now, while you are designing the course.
For anything graded, build a Rubric: a small grid of criteria and performance levels. Attach it to the assignment or discussion so students see the target up…
https://ksarn.org/guide-discussions-and-rubrics/