the cool thing about thumbnails though is that it doesn't matter if they're "crappy drawings".
Thumbnails are like thinking out loud, but with your pen. Especially if you do it for a personal project, noone needs to understand what the f*ck is going on in your thumbnails, the main thing is that YOU get it. it's a way to solidify and hone down your ideas. And if it's a crooked unrecognisable stick figure with a wonky head, it doesn't matter at all, because you know what it's meant to represent and when you look at it a few hours down the line, you'll still know what it represents. Visual reminders are very powerful.
long story short: just thumbnail away! no drawing skills needed! ;D
Agree, just sketch and get messy!
I like it.