Promotions come when the admins think you deserve to be promoted, the most important criteria are activeness, veteracy, politeness, and following the rules.
Academy student - Once you profile is aproved you will be automaticly approved to academy student.
Genins - You start as a academy student, but once your ninja is approved you will be promoted to genin as soon we have a team for you, you just have to wait.
Chunnin - Genins go trought the chunnin exams to be aproved and become chunnin.
Special Jounin - The Special Jounin are promoted by the hokage/ admin.
Jounin - The best Special Jounin are promoted to jounin by the hokage/ admin.
Akatsuki - 10 member limit, must have deserted village/ killed 25 members of own village.
Anbu - Are the best of the best and/or are the ones that the hokage/ admin deems the most worthy to join this group.
Moderator - To be promoted to Moderator you must abide by the rules enough to get an admins attention.
Kage - To get promoted to kage you either have to be really good or get really lucky.
Sannin - The highest rank possible, must be Kage to be promoted, promotion given by hokages/ admins.
Have fun out there guys!
-Lakstick