Some time ago, after I had read what khris had to say about hidden roles, I started to look for those key player roles in my team. For me it was quite easy actually. I already had two key players in my attacking arsenal. I've had a huge amount of luck when signing new players and always getting at least one in active starting XI. It's because those roles are only attached to a player when he is signed, it cannot jump to an existing player. So when I had one active key player, the other was holding his role at the bench or reserves.

So first thing to do is to sell everybody, but your starting XI and three others. Then play friendlies against 1% teams, which will reveal your key players, sell them, and replace them with aml, amr, amc or st. I have all three aml, amr and st/amc who deliver more than 1 goal per game through their careers plus passes. The best retires this season and has a bit under 1300 goals and 800 passes. His predecessor had 1100 goals and 600 passes. I have succesfully passed on these roles 2-3 'generations' now.