I think consistency is the key. Football is different from other sports ( I ran track in college). But it seems like you can either come out flat, or do the opposite and get too amped up and then you wear down and can't sustain it. Controlled focus. Not to get too high or low. Not to dwell on anything throughout a game; good or bad. Do the work during the week, and hopefully if you prepare enough it will become instinctive. If you are well prepared and well conditioned the rest should take care of itself if you are mentally strong. But being mentally strong and physically strong went hand in hand; at least in my sport.