The difficulty you may encounter when drawing a person seated in a chair depends on the angle from which you are drawing that person. If you are drawing a person from the side, your subject is likely to look unnaturally flat and stiff. If you are drawing your subject from the front, the foreshortening of the legs, feet and hands will be difficult to capture. Overall, seated subjects are not simple to draw well. Still, with practice and some confidence, you can make a drawing that satisfies you and the viewer.
Choose the position from which you will be drawing your subject. Then, find a photograph of a person that matches the drawing you would like to make, or take a photograph yourself. The image should be high resolution, and large enough to capture details. Photography is generally easier to draw from than a live subject.
Draw several quick sketches of the figure in the chair. Do these sketches quickly and without too much regard for accuracy, while still making the effort to draw what you see, not what you think you see. These sketches will help you make looser, freer lines. Once you have made these sketches, compare them to the photograph and ask yourself what works, and what doesn't.
Set aside your initial sketches and pull out your art paper. Draw the main segments of the subject to establish the basic structure of your drawing. An oval for the body, connecting, elongated ovals for the parts of the leg, an oval for the head, a segment connecting the head to the body, elongated ovals for the arms, and ovals for the hands. Note that if your figure is seen from the front, then the thighs and feet will be foreshortened. The thighs may not even be visible at all. Draw only what you see, not what you think should be there.
Outline the body to fuse together all the segments in one large piece. Flick your eyes back and forth between your paper and the photograph as you do this to help you draw the outline accurately. If you're drawing the figure from the side, exaggerate the curves of the body to avoid a stiff or flat figure.
Add details to the body. Details should be added from large to small. Don't concentrate on the minute details until you've drawn the larger, more obvious details.
Step back from your drawing and return to it at a later time. Look for inconsistencies or errors, and make alterations as necessary.