from an article from Poets&Writers by Katrina Vandenberg:
The first poem in a collection provides an entry point for the reader, an invitation into the work. The selection in the number two slot is just as crucial in that it shows your reader (or listener) how you make patterns. "Poets sometimes put poems that are too much alike too close together. I like those chimes to have more of an echo," says Jeffrey Shotts, poetry editor of Graywolf Press. This might be especially important at the beginning of a book; you don't want the contract you've made with the reader to be too tightly written. By putting some space between the most obvious matches, a poet can create even more space for herself to move around in.