To Prologue or Epilogue or not...

There are some editors and some houses that will tell you not to add a Prologue or an Epilogue to your story. There are also some readers who will tell you they usually skip reading the Prologue. Given this what is the best way to add a Prologue and an Epilogue so you can assure your editor, publisher and even your readers will love what you have added to your story. 

We will start with hints for writing a Prologue first. 

Keep the Prologue short. If it goes on and on, readers will tire quickly of it. A short and well written Prologue will engage your readers right away if done well. One to three page prologues should be enough to get to the point. A good prologue should include something that isn't shared elsewhere. 

Make the point of the Prologue be very clear. Again it should be engaging enough to capture your readers attention. But ask yourself why the Prologue is needed. Does it push the story forward or give hints about what the story holds in adding to the story. Make sure the Prologue doesn't give conflicting or confusing information. If a reader cannot engage in what is being presented they may read no further. Would your story be complete without the prologue you have written? If so you don't need the prologue or you need a different angle on it to make the story make sense. 

A Prologue should not simply be the start of the story where it seems like chapter one. Most often a Prologue should occur prior to where the story starts or for a twist it might explain something that happens in the story after the fact. As an example, it could occurring 4 months prior to chapter one. Or two years prior to chapter one. But it might also add a bit of intrigue for the reader to have the Prologue explain something and chapter one begins several months prior to the prologue, giving the reader a hint at what might have played out. Or a hint of what is coming when chapter one begins prior to the event described in the prologue. 

A prologue should contain enough action to make the reader engage in what is being planned within the story. But too much action isn't always the answer. If a lot of unexplained action happens without hints of what is to come, the reader may be confused or bored by what is taking place. 

Make sure the characters within the Prologue are up to something interesting enough to keep the reader engaged. It need to make sense to moving the story forward but a Prologue should not be a place to dump I formation or backstory.

Some authors/editors will tell you not to label your prologue as such but to go ahead and make it chapter one. I personally do not agree with this as I mostly write historical western romance where having a Prologue and an epilogue is better accepted. I think it is best to identify for the reader what they are reading. 

Avoid the dreaded dream Prologue. I have never much liked where a fantastic scene or chapter has the character wake up from a dream at the end, leaving me to wonder if what happened is even a real part of the story. That can be for some readers a big point of dissatisfaction. 

It might be wise to have a Prologue that occurred in a different location than where the story takes place. This isn't a hard requirement by any means but can add to the engagement of the reader. 

A prologue should raise but maybe not answer a question. You need to keep the reader wanting more and questions of what happens next can keep the reader turning the page. Readers will want to know they will find put what happens and the promise of that keeps them in the story. A good prologue might introduce the perils or the main problem a character will go through but with only a hint of what will happen. 

A prologue might be in a different POV than the main character of a story to add a bit of depth. Maybe the POV in the prologue belongs to the villain for instance. 

And now let's discuss Epilogues. If you write a strong ending to a story some authors and editors may say an Epilogue isn't needed. An Eplilogue takes place outside the main story and most of the time is after time has elapsed at the end of a story such as a few months later to even several year later. A good Epilogue should add to bring more closure to a story when needed, often time more often used in historical novels. It is not another enhanced ending but should satisfy readers further. 

An Epilogue may serve to further tidy up a story. To enhance by adding things not resolved for the reader in the main story. Often an epilogue may be added to give a hint at how things went after the end of the story. 
The Epilogue needs to be needed to finalize details. Your story should stand alone without it and it's only purpose is too enhance details of the future. It is OK to leave some things open to the readers imagination and not have an Epilogue. it is important to end your story well instead of worrying about setting up a sequel to the story. Yes you may want to hint at a future story but make your ending clear before you worry about showing your readers the details or hints of what is to come.

So an epilogue is best when
For closure
For happily ever after
For introducing a sequel

Just make sure that when writing a prologue and or epilogue that they are truly needed and written tight and to the point.