I hear that agents hate prologues. I also hear that it's a generalization and depends on many factors. Generally speaking, if you keep a prologue brief and VERY connected to the protagonist's background and current persona, is it OK for agents, and would you mention these parameters in the query letter to forewarn the agent? About flashbacks - Should they be included here and there to help shed further light on a specific relationship within the story? What would you avoid regarding flashbacks?
There is definitely a certain animus against prologues in the industry (most likely because so many new writers use them improperly), but since there are recently published successful novels out there with prologues - Christina Baker Kline's The Orphan Train is one - it clearly isn't universal. It also isn't logical, since there are times with a prologue is not only proper, but necessary. Nevertheless, it would appear at the moment that some agents - or, to be more accurate, their interns - may be using the inclusion of a prologue as one of many automatic trigger mechanisms to propel queries into the dumper. A top agent may receive 10,000 queries a year, and they need some way to whittle them down. If your purpose is to present an aspect of your mc's persona, I would advise doing it in other ways within the story itself. If the purpose is to present some aspect of your mc's background, I would only use a prologue if it was something that the mc would be unable or unwilling to recall, thereby making it impossible to reveal through the mc's thoughts. As for flashbacks, use them only if and when they are absolutely necessary to the reader. The great trap of flashbacks is that they can turn into gobs of backstory that the reader doesn't need to know in detail. Good luck.
