By far my most viewed post is about some classroom handouts that I made to teach the elements and principles of design. I have them printed larger for my classroom and I wanted to make it easy for others to be able to order them printed at various sizes, and in higher resolution. They're available for order here:
The Elements of Design
The Principles of Design
A full Elements and Principles of Design Unit plan (complete with lesson plans) is also available on my Teachers Pay Teachers site, here.
The letter-size worksheets by themselves (without the lesson plans) are available on my Teachers Pay Teachers site, here.