I'm still working on kind of a training guide on which order you should train the skills to get the max out of your new young players.

Fact is - I didn't train enough players yet. Fact also is, you need a few more greens on your players than with GK training, especially when you concentrate on the white skills and train one single drill until the average of the skills of this drill are 140%, which is usually when he (almost) doesn't gain anymore from one drill.

Today I bought a MC and tried to develop him in a way it makes sense. He was at 83% and I got him to 113% with about 180 greens spent on him.

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I trained Long Run first, then Sprint and then PGS to get speed to a high level. After that I went for Hold The Line and a bit of Video Analysis. (All clean drills so far) To further improve his tackling and dribbling a bit, I finished it off with some 1on1 finishing. (also increasing grey skill finishing)
There are a few more drills that I could go for at this point. Skill Drill for example, I could go for higher Dribbling and Creativity while having to also improve heading. Or Hurdle Jumps to improve Bravery and Speed even more, while also improving Aggression. Use Your Head and Stop The Attacker are also good options, as they both train 3 white skills and only 1 grey skill.

So there is a lot you can do. But firstly I would always concentrate on the clean drills (the ones that only train white skills) and also the drills that improve only 2 attributes, like Long Run, Hold The Line, Gym and so on. From there you can work your way forward in a good way.