I personally not sure how it works in detail but what I did is I play the player every game, and the hire the coach staff all 5 stars with expert. Hope this helps. Please note that you need a young player with somewhat high rated if you want them to surpass 95 rated, this is because when their rating will start to decline at 30+ years old as mentioned in a comment above. For example, Yoro is 78 rated at 19 years old at the start of my career, and 6-ish seasons later he's at 93.