In order to advance in your ranking, you must complete one of three quests given upon you becoming available for the promotion, not before.  It does not matter how you complete the quests as long as they are completed within the time limit given.  However, there are some penalties that come with ranking.  Upon advancing, if you speak of your quest to that of a lower rank before High Inquisitor Ashetian or one of her officers does, then i will result in you loosing your current rank as well as possibly being disbanded from her order.