I've got to design a poster with the main elements of music on, any ideas.

Answer 1

Hmmm. Using 2D media to describe an aural art. Is that the opposite of using music to describe a painting?

Here is an idea. Use Google to search for
main elements of music,
then click on images to see the images.

Answer 2

You could use notes, clefs, etc. Bob's idea to search first was excellent.

Sra