Mess- Writing can get messy. From the top of my desk to the inside of my brain!
Muck- You have to be willing to trudge around in the muck to discover the true essence of your story.
Mood- Set the mood with the right lighting and background music when you write.
Muscle- It takes real strength to continue to believe in your project and not give up.
Milieu- Know the entire world of your main character, the milieu of emotions that motivate her.
More- When you think you've pushed your character enough, push him some more.
Marvel- This is what I do when piece of fiction comes together with all its requisite parts.
Memory- All your characters have them, it's what motivates them, as the writer you need to know them, as the reader not so much.
Move- Hard to remember but moving every 15-20 minutes could save your eyes and neck.
Mellow- Sometimes a good chill in your favorite chair can loosen the creative juices.
Magic- This is what happens when a story is born.
Masterpiece- We all hope our WIP will become a finished piece of art.
Motivation- Things that get me going: A brisk walk, chocolate, reading a great book or even just a trip to the bookstore.
Do you have any great M-words I've left out?