Add borders to all yours elements.
No matter what is your video about but you should always put borders to your photos. It will surely attract some audience for you
don't add unwanted things.
If your thumbnail is not looking neat and clean no one is going to tap it. so don't paste things that are not needed, The part of thumbnail which is more important to the users should be kept large.
Add a face with expressionsI don't know but why i always prefer a video thumbnail having a face on it. It will be more appealing to the audience, and will be more attractive.
Write the words popping out
Choosing color combination will also play a key factor to make your thumbnail attractive and appealing not only for the images and the background but also the text
Place some negative words in your thumbnail.here negative word doesn't means that you have to put some click bait ?in your video.
just place some words like not no never andn also some interrogative words to ask questions like what? Who etc.
WHERE TO CREATE YOUTUBE THUMBNAILS.
IS THUMBNAIL IMPORTANT