I think the best way to work on my concentration when I just want to be not at my best game and distracted with other stuff, is to just read more. I think reading is the best way to cure my disease for not being able to concentrate for long periods of time.
Also for secondary purposes, I think it's good to work out as well too and try out healthy projects just to keep yourself busy. I guess keeping the self busy and trying to go out of your own to meet more people can be fun. Getting rid of social anxiety is important too, so it can all add up in the end.