Shape a block of modeling clay (sized to fit your sculpture) into the rough shape you're looking for. Since you'll be working with facial features and hair, you may want to start with a bust. This will allow you to focus on those features. Clay is a good medium to use when you start sculpting, because it's easier to work with than stone or wood.
Fill a bowl with water, which you'll use to smooth out the rough edges in your sculpture. Lay your tools out for easy access. A simple set of wooden sculpting tools is all you need, though you can purchase a number of clay sculpting sets and tools in different grades at any hobby store. Tools for clay sculpting are generally simple and come in different sizes to allow you to change the detail level.
Apply the hairline of your human bust with a clay shaper. Don't worry about adding detail to the hair just yet. Use your fingers to form the features of the face: nose, eyes, mouth and ears. Again, don't worry about detail. Right now you want the composition of the sculpture.
Wet your fingers and smooth out some of the facial features. This will give you a fully formed foundation upon which to begin sculpting the details of the facial features and the hair.
Slice thin strips of modeling clay from unused clay and shape according to the hair style you want. Roll and flatten the clay for straight hair, twist it for kinkier hair or curve and curl it for curly hair. Lay the strips of hair within the hairline, arranging them to get a natural look. If you're going for perfect hair, you don't have to stagger and overlap the pieces of clay, but most hair isn't perfect.
Edge in the details of the eyebrows, facial hair (if any) and the details of the eyes with a flat edging tool. Use your fingers to form and reshape as you go and the details begin to add life to your sculpture.
Smooth your finished sculpture with wet fingers. Take this opportunity to blend details so your sculpture doesn't have hard lines. Pay particular attention to smoothing around the hairline to add contour to your subject's face.