Shooting to me has become ambitionless, at least on a good day. Mentally I try to only focus on breathing only. Specifically I try to breath completely normally and in a relaxed manner through a string. This helps reduce anxiety, anticipation, and thoughts about the previous shot. I can't tell you it helps scores, although I think it does, but it certainly changes the whole experience so that each shot approaches the sensation of lasting an eternity.
In order to extinguish flinching and, more subtly, the autonomic fear response one can feel with shooting, I load a revolver with a round, spin the cylinder, and pull the trigger. I try to concentrate only on breathing during this, being acutely aware of any preflinch anxiety. My goal is to have no physiological response when the round finally ignites, whenever that may happen. I find this a very difficult exercise but one that should translate well in improving concentration when shooting in general.