The principles of design are the fundamental parts of an artwork. Identifying these principals is one way to understand an artwork.
#1 - LINE
A line can be described as the path of a point moving through space. In an artwork, there are many types of line. We can look for the direction of the line, the feeling of the line, the quality of the line, and how the lines move our eye through artworks.
Line can be described in many ways:
active - passive bold - delicate
flowing - light straight - curved
thick - thin long - short
broken - continuous geometric - organic
implied - actual precise - irregular
contour - outline vertical - horizontal
perpendicular - parallel zig-zag - direct
Great example of line work in art: