It may be helpful to start by looking at the work of art and identifying the visual elements. How are they arranged? Is the work balanced? Is there a focal point? Is there a sense of movement? You might consider why the artist chose to include certain elements and how each element contributes to your response to the work.
Formal elements possible in paintings/2-dimensional works: picture plane, composition, color (which includes hue, value, saturation, intensity, temperature – warm/cool, primary/secondary, complementary), line (which includes contour lines, lines of direction or movement, line quality), shape, contrast, texture, and illusionistic space.
Formal elements possible in sculpture/3-dimensional works: scale, in-the-round vs. relief, directionality, line/movement, shape (organic vs. geometric, negative vs. positive space), material, texture, volume, light and shadow, color, and technique (additive vs. subtractive).