What are best practices for Design Elements?

Here's a list of what we recommend for best practices for Design Elements:

Maximize preview real estate by uploading a 16:9 preview, even if your Design Element isn’t designed on a 16:9 canvas.
If you’re uploading a project file, make sure it’s organized well and labeled
clearly. Include instructions on how to use it when possible.
The uploader will allow you to choose sub-types for your Design Element.
If you can’t decide between two sub-types, put it in both.
Certain Design Elements will be more contextually elusive than others. We
strongly recommend including multiple previews to help clearly demonstrate
what it is and/or how it might be used.