Pre-Writing refers to all of those things that you do before you actually start writing. Technically, when you wake up in the middle of the night with an inspiration, that's "pre-writing". However, it's a little hard to prove to your teacher that you have been pre-writing in your sleep!

Here are some ways you can organize your thoughts:

Draw or paint a picture.
Make an outline.
Make a list of all the things you can think of pertaining to your topic or story.
Use a semantic map. (Compare and Contrast, for example)
Make a collage out of magazine and newspaper photos.
Brainstorm with a partner, or with your class.