Contrast is the difference between background and an image or between two elements. contrast is often seen in color shape or size.
Alignment is the placement of visual elements in a piece/graphic/layout in a way they line up visual in an obvious way.
Repetition is the use of same (or similar) elements over and over again in some sort of pattern throughout a design.
Watch; beginner's guide to Contrast
Proximity is when elements go together to create a specific meaning with together. If the element are separated the meaning might go away.
Whitespace is the use of space-white or any other color- to draw attention to a particular element
Hierarchy is is emphasizing the most important elements.
Watch; beginner's guide to Proximity
Watch; beginner's guide Hierarchy