At some point in every aspiring artist's progress comes the desire to learn how to draw the human figure realistically. People are inherently interesting subjects, and command the viewer's attention. It is not for nothing that art lovers are still captivated by the Mona Lisa and her enigmatic smile. People interact with each other every day. Your attention might be caught by a face in the crowd, an interesting stranger across a busy street, and you might wonder what they're like, what they think, what their stories are. People are a curiosity, a mystery, and it's only natural for an artist to want the skill of rendering them accurately to be added to their repertoire. This is not an easy skill to attain, and requires a great deal of practice.
Gather your art supplies and reference material. A regular #2 pencil is alright for light sketching, but for a final drawing you should have several pencils of various lead softness (HB, 2B, 4B, 6B) HB is a harder lead, and they get softer as the number goes up. The harder leads you will use for sketching and outlining, and the softer leads work well for shading. A kneaded eraser is an eraser with a stiff putty-like consistency. It's useful because it can be molded like clay into a small point for erasing small areas. A blending stump is a stiff stick of paper felt used for blending parts of a drawing together. These, along with a sketch pad, can be bought at an arts and crafts store like Hobby Lobby or Michael's. As a reference for your drawing you can use a live model, photographs, magazines or the Internet.
Draw a rough, very light gesture drawing of your model with your hardest lead. A gesture drawing is just a general scribble that blocks out the shape and pose of the model in the drawing. It helps to get the general size and proportions right. You'll be drawing over it later and erasing the unnecessary parts, which is why you draw lightly with the hardest lead.
Draw a basic outline of the figure using simple lines and shapes, again drawing lightly. Don't worry too much about getting it exactly right at this point, and don't worry about detail. That comes later.
Draw light reference lines for the features of the face. Start with a line bisecting the face that runs from the top of the head to the chin. Draw lines across this one that are level with the eyes, nose and mouth. This will help you position and orient the features of the face.
Draw light outlines of the eyes and mouth, and a suggestion of a nose. Check with your source to make sure that these are positioned correctly.
Refine the outline using a slightly softer lead. Draw a more precise contour of the figure, and refine the details. If you're stopping at a line drawing, darken the final outline, and erase the sketch lines if you like. Otherwise, leave it light, so the shading will define the form instead of the lines.
Shade the drawing. Start with the lightest values in harder lead, gradually adding darker shading with the softer lead. It may be helpful to draw an outline of the different areas of shading rather than shading in freehand. Use the blending stump to blend the boundaries of these shaded areas together into a smooth transition between the two values, unless it denotes a shadow with a hard edge.
Shade the hair by drawing pencil strokes in the direction of the hair growth, again starting with the light shades and moving to dark. Use the blending stump to blend the shading smoothly. If you need to lighten it or add a highlight, mold the kneaded eraser into a point and lightly erase in the direction of the hair growth.
Clean up the drawing, erasing any sketch marks that are still visible. Check for any minor details you may have overlooked, or any small mistakes you may have made. Don't be discouraged if you have made any, or if the drawing does not look quite right. It takes a lot of practice.
Drawing realistic people can be a challenge even for someone who has been drawing for a while. If you're just starting out, you're bound to be disappointed or discouraged with your drawing. You would benefit by getting a firm grounding in drawing techniques first, and there are many resources to help you. You can take art classes if they are available to you where you live. You can get any number of art and art theory books from your local library or bookseller. There are even websites dedicated to drawing and drawing tutorials. YouTube is a great resource for drawing lessons, as you can watch the drawing happen instead of looking at still pictures.