When running your team trainings (including training camps) two factors matter:

- The players age

- The players born potential

The born potential is show by the color in the player cards called the player rarity. The more rare a player is the better he will train.

The younger a player is the more he will improve when training. When players are teenagers they improve a lot. From 20-25 the improve some. From 26-29 they improve a little and at age 30 and older they will start dropping in skills once per day and not improve much in training anymore.

You can increase how good a player trains but doing well in the daily traning minigame but not that much. It is all about having those high rarity players at at young age to get super good training output.