The best thing that my PhD advisor did to/for me was to make me review papers (as part of the peer review process). By having to critically analyze someone els

The best thing that my PhD advisor did to/for me was to make me review papers (as part of the peer review process). By having to critically analyze someone else's work, I learned what I needed to do to meet that criteria myself. And, in case you are curious, the first few reviews, he read through and challenged my reviews personally, and pointed out things that I missed. After that, I was on my own. In short: if you want your students to write better comments, then make them critically examine the comments of open-source projects. Their use of comments will improve. Ditto for code structure, proof analysis, test writing, etc.