I am not trying to be glib. I get asked this question every single convention, every reading, nearly every day. I will be asked again. Here is the magic formula: You do not wait for inspiration. You just get to work.
Anyone who tells you differently has not published a novel. All that matters is you sit down and get yourself to work.
That being said, somedays the words and drawing flow from your fingers. You know exactly which words to use and you look back on what you just wrote and think “This is art. This is literature. I am a WRITING GODDESS!”
Sometimes you do a reading of your work and everyone is listening to what you say, they laugh in the right places. You don’t stumble. I remember the day I made my first sale of The Carp’s Eye at ECCC 2008. I still remember the first time in 2009, I learned I had a single super fan then I learned there was twenty others. I still remember the day that I sold my first short story and four days later when I got paid.
However, not every day is like that. You work anyway. You put your butt in the chair and type until your fingers are sore. You have to draw until your hand cramps. I draw every panel by hand, then color on photoshop. My hands cramp up, my back and right shoulder get sore.
Being an author means you are on a constant roller coaster of emotions. You should weep when your protagonist does. You should feel scared. If you don’t, no one will. You have to let your characters take over. You become a vessel for their whims.
You keep writing and drawing. You do it when the days are long and you haven’t sold a book in a week. You have to do it the next day too. And the next and the next until one day you have something. The hours you put into it doesn’t matter. There is no guarantee. So that’s how you write a novel or draw a graphic novel.