A good exercise awakens you to get ready and makes you active for the rest of the day. Even a simple observatory exercise can also charge you up. It is as easy as observing what you see and then putting upon the paper as you want.
For example, observing your family members doing daily chores and capturing their posture in a quick line drawing, would clear the idea of human body proportion. It would also help to study how a human body seems in a perspective, at which places cloths would have creases, movement of other body parts when hand or leg has been moved. This observatory drawing would help to draw human figures more realistic. Moving on detailed study of light and shadow can also be done by drawing portraits.
Starting off by observing proportions, then to light shadow one can practice portraits. At first it would take time to make proportionate drawings. It could be improved by observing the parts of the face with reference to some other parts of the face. For example, the distance between two eyes is about one eye or the ears start at the level of the eye and end near to the level of the nose. These portraits also depend on the quality of the strokes like men would tend to have sharper jawline then women it could be achieved through a bit of straight strokes. On the other hand women tend to have softer cheeks, which could be achieved through smoother strokes. Sometimes these strokes also depend on mediums which have been used. Thus one can practice to improve their skills and understand which medium works better.
To conclude, just by practicing this observatory exercise one can develop new skills, and understanding of the effect of small details in the drawing. Just an hour of exercise in the morning leaves you as an observant for the whole day, hence increasing your observation power day by day.