When hiring a copywriter, I like them to know a bit about SEO - this helps down the line when the client decides that they'd like to integrate that to their site.
Secondly, I like for my copywriter to use their initiative. By this, I mean, I give them a clear brief as to what the vision is, and they need to come up with something creative to compliment my design.
This goes for both online design as well as print design