One pitching coach had my son take this approach on the mound:
Whatever your first pitch is, concentrate on throwing that pitch to that location to the best of your ability. If it works, take the same approach to your next pitch. When, note not if, but WHEN it doesn't work, take an extra moment to "get over it" and then adjust your hat or jersey or whatever works for you as a sign to yourself that the pitch is over and you're ready to move on...Then you begin as if it is your first pitch above...Seemed to help my son reach that state where he had a short memory when things went wrong - either by his doing or someone else's. As a 13U he was the team's #1 pitcher and had 7 complete games...BTW - he's now a lacrosse goalie - another position where you need the same type of short memory approach to your position!