By proving that you are knowledgabe on threads to the members of knowledgeable rank on the site, and by showing you can consintantly follow the rules. Typically people's posts on here make it pretty transparent in telling how well studied they are. The more you prove yourself, the higher your rank.
If you copy/paste that into your browser bar and follow the link, it will redirect you to a thread on the topic. It gives information on each rank and what you can do to work on progressing from one to the next.