Prepare for pressure situations by putting pressure on yourself in practice. Have the same high standards in practice that you have for yourself in games. Allot some time in practice to put on your game face and practice with the same mental and physical energy that you would in games. For a pitcher, it could be having a mentally intense bullpen session. Both Nolan Ryan and Greg Maddux use to react to poorly executed pitches in the bullpen in the same manner and intensity they would in a game. In effect, they are also practicing how they mentally handle a poor pitch in a game, and how they plan to fix it and refocus on the next pitch. Lazily shagging fly balls in the outfield or playing home run derby with your hitting group does not prepare you to play a game or handle clutch situations. When it is your turn to practice, whether you are taking a ground balls from a coach or stepping into the cage to hit, put on your game face. Do not practice your practice habits; practice how you will play the game.
from Mental Toughness-Baseball's Winning Edge