The first thing I recommend you do is make the image the normal rectangular size for a thumbnail. Adding square images as thumbnails can be horrible.
The background should be more than just plain white, and you don't need to write 'by JETINATE'. That will already show. I recommend you show a graph with rating going up bumpily, to show challenges.
This is the thumbnail of a blog post by @CoachJKane. Please make your own thumbnails.
Nice and simple. But why is the chess.com symbol there? I think you should remove that as sure, you are writing your blog on chess.com but it is not about them.
Also, I think there is too much text. Maybe "Top 10 in September" or "September's Best Victories" or something more concise would work better. I don't see how a rook is related either. Maybe include an image of a board with one of your best moves or something like that.
Post your thumbnails here for review.