Your roster ranking is based on your roster score.
Roster score is calculated at the end of every week, and it is directly affected by your show attendance. The amount of points each roster gains is based off the number of existing rosters: i.e: For 10 rosters, the points pool will be (100 x 10) which will be 1000 points total.
The points pool will be distributed based off rosters attendance during that particular week.
Your gain will be equal to = total points x your attendance / total rosters attendance
To simplify this, lets assume a server has 2 rosters competing:
The points pool will be: 200
One show had 1500 tickets sold, while the other only sold 500
the first one will get: 1500 x 200 / 2000 = 150 points
the second will only get: 50 points
Important: If you air more than one show per week, only the highest attendance show will be taken into consideration