Let's talk fears.
Everybody loves that main character who's totally bad-ass, who jumps without looking, who charges head-on into battle knowing that he/she may or may not make it out alive. I don't know about any of ya'll, but I tend to write those characters in all of my first drafts.
When I edit, I add in some fears.
There's those typical ones: the fear of losing the ones you love, the fear of somebody learning a secret, the fear of dying, the fear of not being remembered, the fear of everything you're working for failing. Very real. Very true. Everybody has those fears and if some of the main characters I read about didn't have any of these, I'd be slapping the author upside the head and saying, "Nobody's a robot." You know, unless they are a robot. That could happen.
The fears that I get interested in are phobias. What if your character was afraid of the dark? What if they were afraid of heights? Spiders? Walking on ice (and yes, I can attest to the fact that this one is very real)? Cockroaches?
Here's a challenge for you: take a novel you're working on or have already written, and give your main character a phobia. Dark places, small places, escalators, guns, flutes (I looked it up; that one exists, too). Seriously, go to this site: phobialist.com, and just choose one. What would happen? How would the novel change, how would their relationships change? Is there a moment or a scene where it really is the wrong time for their fears to paralyze them? How do they get over it?