Really. That's all it's saying. If you are someone who, in your life, has learned things and, at some point, teach these things to others and they learn from you, you're a plugger.
That's the kinder interpretation, anyway. I read "Work hard and keep your nose clean" as a symbolic advice, a representation of generic basic learning, a summation of the fundamental things that people should learn along with the precepts of language. If we take it literally, it's the kind of toothless, content-free advice you'd expect from a discount fortune cookie or a robot programmed with conversational phrases but no actual understanding of human communication and they're making a joke at the expense of old people and their too often dissolving minds.
Your humble critic's plugger status: Positive