What is the Blogging from A to Z challenge and where can I find more participants? Right here.

Are your characters properly Motivated? Do their actions make sense to someone not inside their head?
One of the things I like to do best when I'm editing/reading/critiquing/whatever term makes you happy for someone else, is ask why. Why does a character have to do whatever it is that the author has deemed they must do? Does it fit with their character? Does it make sense?
This might mean the stakes need to be increased or more conflict is necessary to drive the character to a specific action. Maybe they're doing an action that entirely illogical but would make complete sense with more set up earlier in the story. Do we need a little backstory or introspection to clarify the why?
To much why can be a sign of a weak plot. Again, not that the story is bad or the idea sucks, but perhaps everything that needs to be there to make the character's motivation a strong one, isn't all on the page yet. I've been guilty a time or three of sending a story off to critique partners before I've gotten all the necessary words out of my head and onto the page. Sometimes, dammit, we're just really excited to send it off for feedback. Which typically leads to the story limping back covered in red ink and then it sits in the corner, staring glumly at the floor for a few days. Poor thing.
Things to consider:
Is this character under enough pressure to have to make this terrible/major choice?
Does event A, B and C add up to a logical reason why the character acts this way?
Is the character taking an active role in what happens to him/her?
You definitely have some work to do if: The character is acting erratically because...
they had a bad dream or a bad feeling with no further elaboration
for because I am the writer and I said so. Don't question me!
they just felt like doing something different that day
the prophecy said it would happen like this
Enough about character motivations, what motivates you to write?