Compare the number of fans your team has with the maximum number of spectators the team's stadium can accommodate. If the number of fans significantly exceeds the number of stadium places, increase the ticket price above 5, and check if you have full attendance. If so, you can try to increase the ticket prices by 1 again and check for full attendance. Keep on increasing by increments of 1 until you notice a significant drop (less 10%) in attendance. Then, decrease the ticket price by 1. Attendance may also depend on the opponent your team is playing against. So, it may not be consistent even though the ticket price is fixed to a certain value.
Playing in cup competitions brings significantly more money as compared to attendance.