make sure you have a plot,it basically makes all the story.
1. choose the character's emotions/personality,it needs to match the story.
2. make sure most of the time there would be sad moments,that will make the reader's stomach knot. (im not that good at this)
3. don't forget about the actions,make sure everything gets togheter logically.
i can't tell you a lot cause i don't know what you have planned on the story,hope i helped you just a little. ☺♥️