The links in the article (near the top, 3rd paragraph?) address the concern you raise about identifying frequently targeted behaviors and learning how to change them. It's a good question to ask! The answers I saw in those links accord with my experience, for whatever that's worth.

Speaking from that same experience, you're right that the border between assertiveness and assholishness is not clearly marked, not least because all people and situations are to at least some extent unique. I can recommend only cautious experiment as a means of developing an understanding of how to be assertive without being a dick.