Rhythm: A design principle characterized by a regular recurrence of features or elements.
Proportion: Defined as the relationship of the parts to one another or to the whole, whereas scale refers to the size of a thing in relation or comparison to other things.
Balance: The arrangement of objects that creates a physical or visual equilibrium. Balance can be symmetrical or asymmetrical.
Emphasis: A design principle that gives importance to an area or object to make it stand out and hold the interest of the viewer.
Variety: A design principle that is used to express differences in objects or spaces to counteract monotony or sameness.
Unity: A design principle that produces a harmonious relationship among all the parts of an object or space.
Repetition: A design principle characterized by a regular recurrence of features or elements.
Scale: The relative size of an object as related to a familiar standard, i.e., the human body.
Links:
[1] http://www.takingcharge.csh.umn.edu/explore-healing-practices/healing-environment/are-there-design-rules-follow
[2] http://www.takingcharge.csh.umn.edu/activities/what-healing-environment-you
[3] http://www.takingcharge.csh.umn.edu/activities/what-can-i-do-healthcare-setting
[4] http://www.takingcharge.csh.umn.edu/activities/what-healing-about-hospital