My First Fimfic

Hi Everypony,
Just letting you know that some time in the next month, I'm hoping to start writing my first Fimfic. It will probably be slow going because I do sometimes have trouble putting what I imagine in to words. If you have any advice, it would appreciated.
The story will be sort of a Equestria Girls and Harry Potter crossover. And the main idea for it is this question, "What if Sunset Shimmer was the Girl-Who-lived?"
Let me know what you think and hopefully I can get the first chapter up in the next month