Hi,consider how each season adds 1 year more to your players,and, if you uplevel, cuts a star to each of them,also.
So you have to keep your players trained for competition,taking care about those that will retire at the end of season.

Level 4,5,6 usually have the most number of retiring players,as in lower leagues you have neither so many resources (= tokens ,cash and academy)
to buy many players,nor negotiations to sell your unused players.
So almost all palyers remain to you until retiring.

if you seem to be ok with your players and formation,please mind about orders you give:
do you prefer playing defensive(High defensive), offensive (High offensive) or normal?

Which other settings do you make to prepare your matches?