As you'll know if you're a regular visitor to these virtual parts, Rob A Mackenzie and I swapped manuscripts nearly a fortnight ago. I've had a read-through of Rob's MS and will comment properly on it in due course, but suffice to say for the moment that it's very good and a lot of fun in places.
Meanwhile, if you're interested in how one might put together a poetry manuscript, you could do worse than visit Rob's series of posts related to the process. Be sure to read the comments streams. The latest of these posts muses on the relation between what gets into a magazine and what gets into a collection. It doesn't particularly mention how changes in one's own writing affect these choices. For instance, the MS I swapped with Rob doesn't contain my most published poem, with which I chose to open Tonguefire, because it no longer feels to me like a piece of my writing.
Of course, this is connected to the notion of voice, a discussion of which is developing in Rob's posts. Some poets develop single strong, distinctive voices. John Burnside comes to mind in this regard; he has developed a style that is a cartography of a mind. It's a highly wrought object that he burnishes further with every new collection; a single poem extended throughout his writing life.
Other writers cultivate range and variety. Edwin Morgan is an obvious name to drop here, as is WN Herbert. Don Paterson might also fit into this category to a certain extent. Certainly, any of us who write in more than one language will find variety creeping in.
If a published collection is a public representation of a poet's development to date, the question that the writer and editor must ask themselves in putting it together is whether and how a given poem fits into not only the development but the representation. It can and should only ever be partial. After all, I don't imagine that any readership I might have will particularly want to read what I wrote on my off days. Therefore, a good sense of the picture one wants to present to the poetry reading world is probably helpful.
For my part, I feel more inclined towards range and variety than the single voice. That's what I hope to cultivate, and I think I've had some success in my most recent writing at least. But there must still be some sensibility to connect the various voices, styles or approaches. I hope I've achieved that as well, but only time and the reactions of readers will tell.