Before training please, always, test players to oversize the internal programming, so you dont waste resources in players that will have no developement.
2 equal players, same age same all, STs one with 5* and the 2nd with 8*, the one 5* can score 40 goals, and the 8* cal score only 3 goals in a season cause the internal programming settings, so always, oversize the internal players programming by testing players, and if he's well programmed, then, invest resources on him.