Get each player on your team between 48-60 minutes of playing a time each week and it should go up. It only goes up to proficient/prominent though. Just as long as they are in the strong+ range you should be good.
Just to clarify this, GS is actually likely to dip a bit if you only get 48 minutes. There's a nice post from Josef Ka somewhere in BB-global with plots, but i think you generally want to be in like the 56-66 minute range (or 58-68, or something in that ballpark).