Study some of the Mannerist painters like Jacopa da Pontermo, Agnolo Bronzino, Parmigianino and Rosso Fiorentino.
Notice the subject matter. Artists emphasized the intellectual. Use of Christian and mythological iconography, proverbs and folklore are common.
Look for subjective expression. The expressions of the figures are psychological, sometimes tormented. Spirituality is emphasized and yet a seductive undertone exists.
Consider the use of space. The composition is crowded and not as realistic as during the Renaissance. Space is flattened and compressed. Perspective is not as important. There is a blurring of boundaries, creating infinity.
Note the proportions of the figure. The painters distorted their figures and used exaggerated poses. The figures are lengthened, twisting and often in strange body positions. Often the heads are too small for the bodies.
Recognize how color is used. It expresses emotion. The use of color is bright and arbitrary. Colors often clashed and lighting is sometimes harsh.
Observe the details. Mannerist artists are technically proficient, having learned from the Renaissance masters. You can see the evidence in the surface details, coloring and technical aspects like foreshortening.