Tip #446: The middle

Your protagonist and antagonist don’t know when they’re in the middle of the story... they should be doing everything they can to end the story on the very next page

http://kevinkruse.com/9-writing-tips-from-thrillerfest-2013/

But they're held back by something (maybe a character flaw such as recklessness, or a lack of certain information about the problem or antagonist - usually a combination of things).  So they're making mistakes, mistakes which have consequences.  Often unpleasant consequences.  But these mistakes and consequences and how the protagonist deals with them eventually teach the most stubborn protagonist about the thing which is holding them back (often after their biggest mistake plunges them into the Dark Point).

Tip #445: Why character choice matters

There are very few situations where every human being on the planet will respond the same way, so the cascading series of unique choices they make — each time altering how the story goes — is what makes them — and the story — come alive.

When you’ve done it right, you’ll look at your story and realize that it would have been an altogether different story with any other character in the same situation.

http://www.aisteach.com/blog/?p=1205#more-1205

If you have some situations but no protagonist/antagonist, those situations (and how the characters got into and get out of them) help define your characters.

If you know your characters try asking yourself occasionally what they wouldn't do, and then work out why they'd do it.