I won't say that thumbnailing is my least favorite part of the process, but it certainly is one that I seem to shy away from. Trying to come up with ten solutions to an illustration problem of concept, design and composition is about like pulling mastodon teeth for me.
Many professional artists/designers will create upwards to 100 or so thumbnails before they begin to narrow it down to a design that will work. For me, ten is pretty good.
While sitting at my somewhat tedious "day job" I cobbled these thumbnails & sketches together on notebook paper & smuggled them into my pocket before the company secret agents came and handcuffed me, escorting me to a very dark room with a chair and a blinding light.
My thumbnails are usually very rough explorations of form and placement of elements. I don't worry too much about the actual look of the objects because I already have an idea of what they'll look like anyway. It does help to look up reference ahead of time because it gives you more confidence in the placement & size of certain parts of the image.
As you can see (or hopefully you can see) early on, I'm trying to establish perspective. So far I've been going with one-point perspective with a vanishing point on the horizon, located using the Rule of Thirds. You might also notice that I have some significant rock formations in the background. This is where reference comes in handy. At this stage I just did a simple Google search for "Utah rock formations" and took a good look. Don't copy reference, just make mental notes of outstanding characteristics of the reference material. Later you'll have a better idea of what you want to draw.
I also searched for vintage motorbike reference which will be an important part of this piece. Above you can see that I've made a lot of notes on what I want to include in the painting, as well as just general brainstorming about technique/mood/lighting - just all kinds of stuff.
That's all for now. Next time I'll try to share some finished sketches!