I start with a main folder for Teachers Pay Teachers. Inside that folder, I break it down into some categories: Marketing, Completed Products, Products to Finish, Data, etc.
I then break each of those folders down. For example inside the Completed Products Folder is a folder for each product I have created. Inside the product folder is a copy of the product, a copy of the preview, and the editable pieces for the product.
In my Design Tools folder, I have a Clip Art for TPT folder. Inside are several category folders including graphics, photos, borders, etc. I keep each product together inside the category. I don't group them by theme or artist.
I did change the folder preview to the clip art preview to help me find things easier. On my Mac, I use Image2icon, which is a free download, to change my folder preview.
This keeps me organized. Of course, I am terrible at putting things in the right folder when I download something. So every now and then I have to go in and clean up my folders. In fact, it is time to straighten them up.
I encourage you to find a system that works best for you!