The
Boy Scout slogan. Different than the
Boy Scout motto,
Be Prepared! to "do a good turn daily" meant to do something
positive, at least
once to offset all the
awful shit you did the rest of the day. This is embodied in
popular culture by the image of
helping a little old lady across the street.
It probably didn't mean anything you would do while driving, since most Boy Scouts are not of legal driving age.
It surely does not mean "turn a good trick daily." That's something else entirely.