Once you do this enough times you'll get sick of it and learn the importance of planning out your plot ahead of time.
All you really need to start with is to scribble down a bit about your main characters, the setting, and then what their major goal is, what obstacles they'll face in getting there and how they overcome it. That's all the basic elements of a story right there, like the framework that you build a house on.
A good main character will have a character arc, meaning the difficulties they face will make them change and learn something over the course of the story.
I believe Northwind wrote you some kind of ridiculous and exhaustive text wall on this subject in one of your previous threads.