Bryna over a The Everyday Epic just wrote an interesting post called "Rules of Writing (Inspired by Pixar)."
A few of the rules she linked to seemed particularly important.
#6: What is your character good at, comfortable with? Throw the polar opposite at them. Challenge them. How do they deal?
This is one thing I tried to do in the last story in the mystery book – get Jan Sleet out of her comfort zone in a couple of different ways. I think that makes the story even stronger.
#8: Finish your story, let go even if it’s not perfect. In an ideal world you have both, but move on. Do better next time.
As I talked about last time, it is a disadvantage of e-books that you can revise the same book(s) basically forever. As with many other things, just because it's possible doesn't make it advisable.
#13: Give your characters opinions. Passive/malleable might seem likable to you as you write, but it’s poison to the audience.
I think it can be very limiting to aspire to your characters being "relatable." As I've pointed out before, Sherlock Holmes has been (by far) the most consistently popular fictional character in the English-speaking world for the last 100+ years (prose, stage, movies, TV, radio, etc;). He is not passive or malleable. He is not in any way average. He has a lot of opinions. This seems to be fine with the audience.
#17: No work is ever wasted. If it’s not working, let go and move on – it’ll come back around to be useful later.
Very true. Stevie One was my third attempt at telling the story of two of the characters. I think I finally got it right, and it was the first two attempts that helped steer me in the right direction.
#19: Coincidences to get characters into trouble are great; coincidences to get them out of it are cheating.
I don't think I've ever seen this put so clearly. Also, the first part goes along with the great rule of farce (which I've used): the next person to come in through the door should be the person your character most wants to avoid.
Did any of the rules strikes you in particular?

