Creative writing draws on two separate processes. Because they happen in different parts of the brain, trying to perform them simultaneously can literally boggle the mind and keep you from writing anything at all.
First the tree shaking. Jot down everything that comes to mind around your subject: disorderly sentence fragments, memory flashes, tangents and wild goose chases—judge nothing irrelevant, reject nothing. When the first wave of thoughts runs out, don’t stop, but wait for a second wave to build and break. Sit somewhere comfortable with a clipboard. Feel free to write anywhere on the page, maybe on the diagonal, rather than line by line, top to bottom.
Then the jelly-making. Sort through the jottings, looking for surprising images, feeling forhot spots. Can you detect a storyline in the chaos? Choose a starting point and begin to focus on logical and chronological order. This may feel arbitrary; it will definitely mean leaving things out, reserving them for another day. Creating a computer document to allow you to move things around would be useful now.
When you identify places that lack depth or detail, return to the first process of brainstorming to inspire more raw material. Then it’s back to the second process of analyzing and organizing. The shuttling can go on and on, between these two very different mental functions. But always the trick is to tackle them one at a time.