I will definitely try your tips out, having trained as a web designer and thus very familiar with Photoshop, I should already be doing this but honestly my thumbnails haven't been that great. Recently I think I have improved significantly, I keep hearing use click bait, but honestly when I get hit with click bait that doesn't deliver I have very negative feelings about it, so I don't want to jump into that sort of hole.
Also; is it still considered click-bait if you deliver on the promise in the thumbnail? Is click-bait false advertising, or simply good foolery?