Some people will call step one "prewriting." I dislike this term because PRE-writing implies that it happens prior to and separate from the act of writing. Since it is under the umbrella of "writing process" prewriting is, itself, writing. Moreover, it doesn't have to happen before the other stages, as I will explain.
Let's call this step brainstorming. As I said in my previous post on this subject, I don't always follow the preformed pattern of first brainstorming, than drafting, revising, editing, etc. Naturally some brainstorming will come first, but sometimes it is the glint of an idea and then I write a few lines without full understanding of where the story is leading. Then I go back and do more brainstorming, draft some more, edit that, revise a bit, brainstorm, etc. And the sparse lines I first wrote get cut out or tucked away in a hidden part of the book.
When I think of brainstorming, many different activities come to mind: outlining, graphic organizers, research, making lists, and much more. Let's get this out of the way: I am not an outliner. In school (when they made us write an outline) I would usually make it after I had drafted. Like I said, I don't do things in the prescribed order. However, many authors find making an outline first helpful.
Graphic organizers are useful at any stage in the game. When I started writing my first chapter, I realized I needed to know where my character was going and how long it would take. I got out my fresh new notebook. The very first page in the notebook is a map. I go back frequently to update and change the map. Creating calendars and time lines of the plot and characters' movements helps even if I know in my head how long it takes. I also put the phases of the moon on my calendar. That way I'm not describing a full moon shining through a window and then a week later the main character looks up a a full moon.
Research is important for fiction and non-fiction writers. Because stories do not come only from inside the writer's mind alone; they mix the author's imagination with the world at large. For example, I pull from various established mythical creatures to create my story. And while I alter them to fit my own magical world, they are still steeped in ancient stories. I also incorporate the classical elements as a motif, so I researched how different cultures viewed the elements and made an amalgam for my own world.
When it comes to brainstorming all ideas are good ideas. Sometimes it helps to sit down and make a list of all my thoughts on a subject and then filter through to find the best fit. The second page in a notebook is full of various name ideas for the land. I finally settled on one, but the name isn't crucial to the story, so I was able to write with a placeholder for a time. New ideas come at any stage in the process which is why I call it brainstorming and not prewriting. I'll do research and fill notebooks at random as thoughts strike.
Though brainstorming is often the first step to writing, it also happens throughout the process weather you are drafting or revising. Keep open to new ideas as they come and keep a notebook!