These are thumbnails I've done for GameXplain.  Recently, I've been trying to improve colouring with the camera raw filter instead of relying mostly on vibrance and contrast. I've been focusing more on key elements, whereas in the past I would add a million little details.

While sometimes existing assets will work, it can be better to use a higher-quality image to represent the idea for the video. I love it when there's a chance to make it an amusing thumbnail to brighten someone's day. Thumbnail ideas can be collaborative with ideas from team members, or receiving feedback on an initial design.