Tip #308: Easy character arcs

If nothing (and no-one) else, your protagonist should end the story in a different state of mind to the one they began in, unless you're deliberately putting them back exactly where they started to show their lack of change or to emphasise small changes...   

Going from a negative to a positive emotion gives the ending a greater positive impact because the reader is subconsiously aware they've been on an positive emotional journey with the protagonist.

Given examples:

Biggles and Tintin frequently follow this arc:
Boredom -> Increasing Determination -> Satisfaction

Some of the Nancy Drew books often do something similar:
Curiosity -> Increasing Fear -> Relief

The Harry Potter books are much more complex, containing multiple arcs, one of which is:
Alone -> Increasing Friendships -> Loved

H.R. Filmore's Reminders to Self, December 2012

Tip #288: The antagonist (series)

There has to be a Big Boss Battle in your story or the story problem is not fully resolved. A lot of new writers are “writing a series.” And, oh, but Such-and-Such dies in book 12 of my series. No... the protagonist in every book MUST DEFEAT the BBT responsible for the story problem...

your Big Boss Troublemaker... will have emissaries... Depending on the type of story, usually the BBT will have a chain of command...

Book I) BBT–> (Book II) BIGGER BBT–> (Book III) HOLY MOLY! AN EVEN BIGGER BBT!!!!

http://warriorwriters.wordpress.com/2012/10/01/structure-part-3-introducing-the-opposition-2/

In Robert Jordan's The Wheel of Time and J.K. Rowling's Harry Potter books, the protagonist is given the opportunity to battle and defeat a watered-down (but still very powerful) version of the BBT before the final battle.  While they can't be irrevocably defeated until the last book, the plan which caused the protagonist so much trouble in the current book should be pretty much permanently foiled and the protagonist's victory should cost the BBT significantly.