The Decisions stat is one of several mental stats that can't be trained. It will rise naturally as players gain experience, but as Clichy is 27 you probably won't see much improvement.
Most of the 'innate' mental stats - e.g. Determination, Bravery, Aggression, Creativity - can't be focused on in training. You can only train things that can be improved through extra practice, like composure and off the ball movement.