Firstly, there is no confirmation that individual attributes matter and how much effect they have.
To increase specific attributes of a player, you need to be more selective in drills selection (though you cannot be fully specifically selective due to the limitation of the training system provided by the game itself).
The shooting technique drill will improve your ST's shooting and finishing, but will also improve its strength. If you add in a GK in that same session, the GK will improve its reflexes and agility.
You need to read on the description of every drill, and choose them as appropriate for specific training sessions for specifically selected players.