If you are writing a poem, even a non-rhyming poem, you can write it as you would for any other poetry submission. Some authors also write a paginated manuscript, where they submit like this:
Page 5
text
Pages 6-7
text
Other than these two things, double spaced is the standard. It can seem awkward when every sentence is its own paragraph, but it is what's expected and an industry professional will understand this. Note that some people love to see a paginated manuscript while others don't.
SCBWI's The Book is a great resource for questions like this.