When playing at a louder dynamic, it is important to retain the integrity of your tone quality and pitch. Too often, we sacrifice beauty of sound in an effort to attain volume. Ideally, we would like to get both! I have found that playing with a slower, warmer air stream and thinking of playing on the bottom side of the pitch can be helpful. A common error is to blow an air stream that is too fast and play sharp in the higher dynamics. Try your best to avoid this.