The first thing you can share is your exercise worksheet. Here is mine:
I thought the bear hibernating was so cute... This illustration was conceived from mind mapping the word temperature, how awesome is that?? You can do this with ANY word!
This is how I usually use thumbnail sketches:
Here is an example showing the evolution of thumbnail to final illustration for one of my recent works:
Your way of using thumbnail sketching will be different from mine. It can be more messy or more detailed or you could do 100 sketches, or you could use colored pencils only, etc. It's all personal preference! I can't wait to see your process and what you create! :)