The acronym CAS stands for Clean and Simple.
1. Usually only one layer but can include a simple layer or two.
2. A lot of open space sometimes called "white space" can include subtle color, texture or pattern.
4. Usually no embellishments but can include something minimal. (1 or 2 embellishments)
3. Only one focal point. Embellishments should only support not dominate your card.
(Exception to this rule is that you've made the focal point an embellishment and not an image.)
5. Minimal color palette. (up to 3 colors in general)
6. Simple, uncluttered, quick and easy to create.
The acronym CASE stands for Copy and Share Everything.