1)    One should pray the morning and additional prayers on Shavuos morning with motivation and eagerness, so that he will not fall asleep after being awake all night learning. (Ben Ish Chai Bamidbar)

2)    The final stage in the achievement of counting the Omer and learning on the night of Shavuos comes in the additional prayer (Musaf). It is therefore necessary to be very careful about this prayer, for everything follows the ending. (ibid)