Answer: You start with a idea for a plot, then you work out an outline from there. Also, develop relatable characters, making sure to give them each a distinct personality. What do they like to do in their free time? Do they have a phrase they use a lot? Avoid making your character seem unflawed. Also, avoid overused tropes, like dork + popular kid, bad boy meets a girl who changes him, or someone suddenly finding out their the "chosen one". Look up more overused tropes to get the idea. Oh, and avoid the story starting with an alarm going of or the lead character oversleeping.
But the most important thing its to believe in yourself!