Here's what I would suggest for a poster. Have a poster that has two layers, the top layer being able to open up, like a set of double-doors. So, you would get two posterboards, and cut one in half, and glue the right and left edges on top of the first one so that it opens up like a door. Then, on the top layer, put a collage of very beautiful people. Find models, male and female, and glittery beautiful things. That way, when we look at the poster, on the surface layer, it is covered with pictures of people and images that we all envy because they seem beautiful, successful, happy and perfect. But then, when you open the flaps, put ugly, unhappy, dark pictures. Make a collage with words that say "unhappiness", "don't judge a book by its cover", and pleas of help. So, when you go under the surface of the beautiful people, to what is inside of them, you realize that they might be miserable. Does that makes sense? I hope so.
This all can represent the theme of the poem-how surface appearances are deceptive. The poetic devices in the poem are rhyming, metaphors ("waited for the light" a metaphor for a relief from hard, dreary, every-day work), imagery-using the five sense to describe something ("he fluttered pulses" and "glittered when he walked"). You could write those phrases on the poster somewhere, if you want to represent them.
I hope that idea helps! Good luck with this assignment.