Training advice please

Hello could someone explain training players to me please I simply don't understand it. What I do is train on my players on the same setting which is training match. To get the best trains do I individually assign trainers to each position and change the setting or do I just change the whole team setting every now and again?? Any advise would be helpful

Personally I have a trainer assigned for each of these groups, Keeper, defender, midfielder and attacker and then I have a trainer for specific players depending on how they are trained when purchased or if I have players I want to train a bit different.

This ensures that I don't need a huge amount of trainers, but can still train some players the ways that I want.