Find the conflict.
Not every comic book story starts with conflict. Some creators look for places to start that are non-intuitive like the ending of a story. Check out your favorite comic. Open it to the first pages – what do you see? You will start to notice that almost all stories begin with conflict. Now sit down and take your own characters (or invent new ones) and imagine them in the same situation. What happens when you put these new characters in a similar conflict? What elements need to change to make sense?