He, the story writer, doesn't want to end up as another person living the "American dream" of having a pointless job where the only escape is alcohol. Getting "promoted" to sales is basically a dead-end job, and is often the butt of a lot of jokes. The story writer wants to avoid this fate, so he's going to "get his s--- together" and do something with his life.
The point of the song is this:
He, the story writer, doesn't want to end up as another person living the "American dream" of having a pointless job where the only escape is alcohol. Getting "promoted" to sales is basically a dead-end job, and is often the butt of a lot of jokes. The story writer wants to avoid this fate, so he's going to "get his s--- together" and do something with his life.