Thumbnails are a cool tool.....
As artists we tend to start with a single idea, sketch it, refine it, and polish it You invest your time and feelings into one concept and become attached to it, and it becomes harder to engage with other ideas. For most of us the first sketch will be generic and heavily influenced. Even if we make several initial sketches we have often already decided in our minds that the first is the best, and the others are just fill-ins to make up the numbers.
The more variation in sketching, the more critical comparisons you can make.
You don’t need to spend much time on this! Often you only need an hour or so to generate a variety of basic ideas.
This advice from Designshack is spot-on, you may recognise yourselves here!
Cool It on the Details, Picasso
Some of you out there are sketch artists. You’re never happier than when you have a pencil in your hands. Others are truly horrid with a pencil and can’t produce a decent sketch to save your life.
For the first time ever, the latter of these two groups might actually have an easier time! If you can’t draw, great, you’re perfect for creating thumbnail sketches. Talented artists tend to have trouble with the idea of going fast and not really fleshing concepts out. It’s often the case that artists spend more time generating fewer thumbnails simply because they can’t help but make sure every line is straight, every circle is perfect, etc.
Just remember the key at this step is quantity over quality….just make sure that you remember that your goal is to get all of those ideas out of your head and onto paper. For example, if you can draw a box and later remember that it represents your headline, then skip the laborious lettering.
Keep Moving Forward
Another thing to keep in mind is to avoid spending lots of time tweaking an idea to get it just right. If you start sketching one of your ideas and realize that you hate it, resist the urge to erase it and start over. Simply trudge through it and move onto your next idea. Maybe in a few hours you’ll look back on that sketch and see a solid idea in there.
Don’t Draw the Same Thing 50 Times
When faced with the task of producing so many thumbnails, your first instinct will be to start several tiny variations of the same idea. This is often a worthless practice when compared to the value of focusing on truly unique concepts. Try your best and push your brain to produce concepts that are as different from each other as you can manage. Remember that this is the brainstorming stage so there aren’t any bad ideas. Go crazy, think outside of the box; be weird!
From here, you simply let the ideas flow. This is not a practice for honing your drawing skills, instead your focus should be on idea generation. Thumbnail sketching is quick and perhaps even somewhat sloppy. Use basic shapes and don’t spend too long on a single image, as soon as you can get a feel for what that basic layout idea might look like, move along.
http://designshack.net/articles/inspiration/close-photoshop-and-grab-a-pencil-the-lost-art-of-thumbnail-sketches/ for the rest of the article.