Considering that I mainly write fantasy (and dark fantasy at that), this particular piece of advice may seem strange. But, I've found that it's more often true than not.
No, I'm not saying that I've actually met vampires, werewolves, or any other of the creatures that are fantasy world staples. And before you decide that my "eccentricity" just flipped the switch to "lock the doors, hide the knives, and break out the Thorazine" insanity, hear me out.
Even in pure fantasy, you can find a way to weave in things that actually can or have happened. Sure, the people in question might have to jump species for it to work in context, but the reality of the situation can make your story all the richer.
When I was about 14 or 15, I almost drowned. I was on a school trip to a local lake and the chaperones (who learned by the time we were 12, and ditched them en masse in downtown Dallas, that they were fighting a losing battle) were no where to be seen. A group of us waded out to the pier in the middle of the lake and were being typical teenagers. (Translation: we were being idiots.) We used the pier beams to shove ourselves down into deeper water and then bobbed back up... at least those of us who knew how to swim did.
I was not one of those who knew how to swim.
Sadly, when a group of teenagers gets together for the sole purpose of being stupid, they don't notice when one of said dummies doesn't surface with the rest of the group. Nor do they notice their non-swimming classmate has gone too far down to get back to the surface.
The strange thing is that when you're in that situation, you don't realize it, either. At least I didn't. Everything faded to black except the sun overhead and the oxygen that went with it. Since I'm still around to type this, you can assume I hauled by soggy backside out of the water before I passed out. (in fact, I never even told anyone there what happened).
This was the 2nd time I almost drowned while not being able to swim. The 1st was when I was 3 and found out the hard way that humans can't breathe water. Even that little, the same thing happened. I just focused on getting out of the water.
Those two incidents have found their way into my writing.
It doesn't matter that the book in question involves monsters that don't actually walk the earth (or swim beneath the oceans), the scene that resulted is one of the favorites of people who have read it, and I'm convinced that it's because personal experience comes through in the presentation.
I think most writers would agree that everything and everyone is potential novel-fodder. Listening and watching to the way people speak and move is a vital component to any story. If you get it right, no one's going to notice, but I guarantee that if you get it wrong, everyone will. Falling out of a natural cadence sticks out like someone stumbling through the pronunciation of a 2nd language - you might get your point across, but it's no fun for anyone involved.
So, go ahead and turn your most hated teacher into a Gorgon. Make your terrible neighbor into the life sucking zombie he's always acted like. And never underestimate the power of an unintentional punchline.
Someday, I'm going to find a place to use one of my grandmother's golden words. Upon meeting my cousin's fiance for the first time, Nanee sized her up and said: "But that wasn't her name the last time."
Off the cuff and both cringe and laugh worthy. Now, all I have to figure out is how to give that line to a werewolf...