In his address to the candidates contesting the student council elections the Principal said, “If you want others to take you seriously then you must __________ on issues like gender bias and…

To "walk the talk" is to act on what one says, which is what candidates must do on gender bias and inclusivity to be taken seriously. "Rule the roost" means to be in charge, "go around the bend" means to go mad, and "read the lines" is not the idiom ("read between the lines" means to find hidden meaning).