Traditional Chinese Medicine (TCM) associates the season with letting go. It is a time of reflection. A time to ask yourself what emotional baggage are you holding onto that you would benefit from letting go? Letting go of this baggage will make space for more positive energy to flow in.
TCM also associates the season with the lung/large intestine organ pair; with the lungs being the Yin organ of the pair and the skin being considered the third lung. If you notice a rash or a cold coming on it's possible that your lung Chi is out of balance. A Yin routine that incorporates some back-bending poses (Sphinx/Seal, upright Swan, Saddle) is a good way to stimulate your lung chi. In addition, consider using a Netti pot to clean out the nose; the opening to the lungs.
With temperatures varying from day to day, even hour to hour some days, it's a good idea to carry a sweater to protect you from the instability of the season. It's also a good idea to watch how much dairy you consume as dairy is known to cause excess phlegm in the lungs. Cora Wen suggests eating cooler foods such as whole grains, squashes, pumpkins, root vegetables, apples, pears, kidney beans and tofu to help keep the body in balance. She also suggests using honey, cinnamon and ginger to warm the internal body.
It's important to take care of yourself during this time of transition so your body is prepared for the winter season. Practicing Ahisma (nonviolence/compassion) with yourself during the yin seasons (fall and winter) is very important to your overall health and well being. Don't push yourself too hard; take time to rest and relax and laugh with friends. A meditation practice focused on watching the breath could also be helpful as the breath is the link between the body and the mind and helps to regulate the nervous system.