"Go, go, go!," or an instruction one may or may not want to follow for the answers to the starred clues (4,2,2)
I believe the answer is:
step on it
(Other definitions for step on it that I've seen before include "Go faster - put foot down" , "Informally, hurry or drive faster" , "improve rate of advance" , "Hasten" , "Hurry up, put foot down on pedal" .)