Writing Music

Hey there, I'm writing a musical right now and I want to do music composition but I'm not amazing at stuff like that. I have been doing piano for a while so it should be easy for me if you just give suggestions. I have the vocal notes but I want there to be a few instruments playing in the background so I was wondering if anyone knew a structure like "woodwinds should be playing 2 notes higher than vocals and adjust by the octave for the instrument."