Confirm the time and date you are to throw out the first pitch of a baseball game. You should be given at least a couple weeks to prepare. While it's not mandatory that you throw out a perfect strike, it's best to prepare if only for safety reasons. You can injury your arm by throwing a baseball if you haven't prepared for the throw.
Set aside a couple days to practice. Get a baseball, a glove and go to a field with a friend. Start off throwing to each other from about seven feet away to loosen up your arm. As you get comfortable, get further and further apart. Limit your first session to about fifty tosses, and don't throw harder than what feels natural. If you go out to practice again, you can increase the number of throws you do the second time.
Arrive early to the game. Throwing out the first pitch occurs before the official start of the baseball game, so show up to the game at least an hour early. Before you go to the pitching mound to throw out the first pitch, warmup your arm by playing catch for a couple minutes.
Remain calm as you walk to the pitching mound to throw out the first pitch. When you are ready to throw the ball, throw it using the same motion that you have practiced. Wave to the crowd as you leave to the mound.