that is really good advice i must add. i had to do the same thing with my comic 'did you water the flowers' when i finally found the story that made the most sense and i said ok this is going to be the story. as im making the story im still making up characters, im still writing out and fixing parts of the story im still doing all of that but it took me a long time to just say ok its time. i have my story, main idea and main characters the longer you wait the longer it will take for your tale to be heard.
best advice i heard on art was just to do it. what ever your trying to study or practice it doesnt matter how bad you draw ir or how good you are. your trying and learning and thats all that matters. alot of people get deterred from getting into art because they think all artists where born drawing like that that and no one is. everyone, even the masters like the likes of da vinci, picasso, michelangelo all started out with their art looking like garbage. but they studied, practiced, stood up all night perfecting and obsessing over their creations.