Any good craft needs a toolbox. If you're a designer, your toolbox is style, which unfortunately you can't put into organised drawers. This graphic, however, lays out your basic tools as a designer.
The image, courtesy of Creative Market, demonstrates design elements such as lines, texture, dominance, balance and more. Each one comes with a general tip on how to use each element. It's not a full education on each one, but it can give you a starting point if you're just starting to learn, as well as a refresher later.
10 Basic Elements of Design [Creative Market]