Every writer has a different writing process. Some writers need more time to make notes and outline than to draft. Others need to create well-developed characters before starting chapter one. Still others may need only the general concept, and they’ll dig deeper into it while writing. Other writers just write and see what happens. You get the idea.
Learn your own writing process–what works best for you. Whether you need to spend more time outlining (if at all), developing characters, organizing themes. Whether you find it easier to focus on the details or to start with concepts. Whether you need lots of notes or only general ideas. Discovering the writing process that suits you best will take time and experience—and failure, but all this pays off. Because once you know your own approach, you can be flexible in non-essential areas and prepare adequately for a project.
For instance, I’m the planner sort. (Can you tell? 🙂 ) I need to know the general concept of the story, the conflict, and the conclusion of what I’m trying to say (see this post for further explanation of those points). I also need characters developed pretty deeply before drafting. And I’m definitely an outliner. It took 10 years, a lot of trial-and-error, and about 7 abandoned or paused stories to figure that out—but now that I know, developing and planning any story is much easier!