I'm trying to write a song...?

I already wrote the lyrics, and I'm working on the tune and rhythms for the melody, but I want to also create the layers of the song. I want to have the vocals, the drum set (with b drum, snare, and crash cymbals), and I want to have the guitar and b guitar too. What other layers could I add to it, to actually make it sound like a professional song when I put it all together? Should I have like a keyboard type sound, or something else?