Satisfaction

Plotting a stories ending is the light at the end of the tunnel. Writing the story to the point of reaching this 'light' may involve a number of twists and turns, but knowing where you are going as a writer generally allows a return to the plot arc if you find yourself lost. With that in mind, ask yourself this question:

How is the story I'm working on going to end for my protagonist?

I did a little digging and found some gems:

The knee-jerk answer is generally something like this: "For any story to have a satisfying ending, the protagonist of the story must end up in a better, happier state than he or she began the story in."

That's all well and good; it gives the reader a sweet sense of satisfaction after the trials and tribulations found on the road of the stories main arc.

However...

Characters May Affect Change: Your character may change his situation, his environment, and thus put an end to the conflict.  This is the classic tale of the hero overcoming cancer, the hero putting down a mutiny, the cop catching the bad guy, the farm girl marrying the handsome landowner, and so on.

Character May Change as a Result of Conflict.  In this ending, our protagonist is permitted to lose, so long as he or she grows from it.  So the kid dies from cancer, but learns to grow and accept death in the process.  Or your hero walks the plank, loses his ship, but is better prepared for the signs next time a mutiny is about to break out.   In these cases, the growth of the character becomes more important than winning.  Even though the battle is lost, something is salvaged from the incident. The protagonist learns how to live.

Your Audience Can Be Changed by the Story. Perhaps each of you can dig back into your own lives and find events, books or movies that have dramatically affected you.

Why do more short stories than novels end on tragic notes?

Lazy writers not working on going for the 'fix'. True tragedy requires finesse and irony in a cautionary tale resolution (these are the 'sucker punch' stories).

How do you keep an ending from being predictable or boring?

Surprise is not always about what happens, but it can be as an unpredictable (but logical) emotion or an emotion far more powerful than expected.

How do you write a stand-alone ending with sequel potential?

Don't kill everybody.
The world should be larger than the story.
The villain's world is well populated.
What type of series is this? Will each book have an immediate follow-up or will one or more generation have passed? Will each book have unique protagonists?

What are the best ways to avoid info dump endings? (the original Psycho's last 5 minutes)

As a writer, stay interested.
Info dump becomes an appendix.
Go back and resolve the info dump 'chunks' in earlier periods of the story.

Are there differences between writing endings for the first novel in a series and other novels in the series?

You've got more endings as you end more books in the series, so you've practiced and have become better at it. Keep an eye on the Mega-plot that covers the entire series. Wrap up everything from the beginning of the book, but not the 'question' set at the beginning of the first book (save that to end the final book).

How do you know which questions to leave unanswered?

Don't let the first book be boring. You can tie things up in a nice (broken) bow, but the bow will have to be untied and fixed in later books. Don't hold too much back for the sequels. The first book should answer questions DEEPLY, but then long-range issues become forefront.

What sort of attention do you give to your last lines?

How can you make sure the ending is working. Leave the reader with an image / phrase that ties up the plot / theme. Connect the two most important characters. Look back on the emotional resonations / beats and echo the pattern in the end. Humans love echoes (it makes us feel smart). Go back and create an opening sentence that reflects the closing sentence. The first line is part of the sales pitch to the reader to read the book... the last line should tell the reader 'thank you for reading'. Encapsulate the irony.

Hope this helps!
-Dave