Falling on your face

For an interesting explanation of Moshe and Aharon's falling on their faces, which happens a number of times in Sefer Bamidbar for unclear reasons, see here.
In short: People fall on their faces when they notice a Divine revelation, lest they see God and thus die. Moshe often falls on his face when no revelation has yet occurred. He does this as preparation for a revelation he hopes will then happen, because such a revelation would be an effective answer to the complainers or rebels he is confronting.