Who is going to do what? Is it an arrangement where one works on melody and the other lyrics? Is it an arrangement where one comes up with the ideas while the other forms the actual words? Does each collaborator write parts of the poem, as with renga? How will you work together? Face-to-face? Internet? Phone? Who gets top billing? Is it an equal or unequal relationship? Is one a teacher and the other a student? Think about the other things that will affect the relationship, and get them nailed down up-front.

It also could be a good idea to re-evaluate the agreement periodically if you collaborate on more than one work or on a very long work.