This ground-breaking study found that the position of your tongue in your mouth can influence power production in isolation exercises. Pushing your tongue against the roof of your mouth resulted in significantly greater power production than other positions! More research needs to be performed to see if this effect is useful in other types of exercise/movements.
di Vico, R., Ardigò, L. P., Salernitano, G., Chamari, K., & Padulo, J. (2013). The acute effect of the tongue position in the mouth on knee isokinetic test performance: a highly surprising pilot study. Muscles, Ligaments and Tendons Journal, 3(4), 318.