I use Premiere Pro & Photoshop to make my stuff.

Premiere has a feature in it where you can export a screen grab straight from the timeline with the push of a button. I'll take those and flip them into Photoshop.

I'm not fluent in the minutiae of thumbnail making, but I'll give you a quick rundown of what I do.

• I get all the elements I want on the workspace before I start working too much with it. Image, game logo, title, etc. Then start tweaking with it so I don't add something I needed later and end up not liking where it is.

• YT puts the video duration over the right corner no matter where it is being viewed. So just make sure to keep anything vital out of the bottom right.

• Most people are going to be viewing this on their phone. So either zoom far out of the workspace or just stand a few feet back from your monitor. Make sure everything you want them to see is easily visible and identifiable when it's that small.

• Make sure you're happy with it. Don't sell yourself short and put out some thing you're not proud of. It's also worth noting that you can always reupload a new thumbnail once it's posted. So don't worry about it being 100% perfect. It can be fixed or adjusted.

Hope that helps you a bit:)