One of the most important abilities in guitar playing is to know how to concentrate.
It is hard to concentrate on nothing, so I use memory to focus my mind while I am playing.
I make sure that everything I play for other people, I can play in my head. The more complex the piece, the more I concentrate on the notes to come.
I take advantage of many moments in the day to run through parts of my repertoire.
For example while waiting in a queue, in the train, in the airplane, while out jogging...
Here is a drawing my father made of me concentrating when I was 17 years old.