Hello
@Niki Proshin,
I get a kick out of working on my own thumbnails as well. It just feels great knowing they were made by you. I'll tackle each image in a separate paragraph with my thoughts. But before I do one thing you should always remember is that when people do searches the first thing they see is the thumbnail thus if thumbnail doesn't convey what the video is about the title may not matter as much. Some people use text and others don't, it depends on their style. But the thumbnails should always hint at what the video is about because people always see the thumbnail before they read the title and may not even bother reading the title if the thumbnail doesn't catch their attention first. With that said...
Your first image looks good. It shows what you are trying to accomplish in the video and the text has a question that can pique people's interest.
Your second image looks good but your question and the image lacks what the video is about. Not do what? There are so many things one should not do but if I'm not, say, interested in cars then why would I care about a "you shouldn't do this" about cars? But I wouldn't know cause they image doesn't convey it's about cars. And if someone clicks and they don't have any interest in the topic they might leave immediately and clicks with low view times can hurt your analytics.
Your third image also looks good but I would suggest movie the text a bit lower, away from the edges of the thumbnail in case they get cut off a bit, and then the text looks weird. Also not sure putting some of the words behind your head, while a cool effect, wouldn't be good because remember that thumbnails are often small even on desktop browsers (and especially on mobile devices) and thus can make it harder to read the text.
These are just my thoughts. Hopefully, they can provide some help.