My tip for stay calm and focus listen to this 3 tips.
1)Using j4k glove for a better filing with the ball.
2)In the locker room Stay silent and listen to the coach and focus to the match.
3)when do you warmup dont do to much thing do exercise for the upper body and the lower body and then i always do some match situacion.
Im sorry for my english,i hope my tips helps for your focus and calm before the match.