As said above, everyone is different. Besides physical things mentioned above to stay warm and loose, get off your feet and rest. Think about the good pitches you made the prior inning. Know where the other team is in their lineup and the game situation. Think about what pitches you threw them last time. Talk to the catcher if he is not hitting on what he is seeing in the game. While sitting down and resting, focus on your breathing. Slow breath in on a four count, four breaths out on a four count. Get mentally ready for the next inning.