Take pictures of the person you will be making the bust of. Take three pictures: one of the front of their face, one from either side and one from the back. Print the pictures out or have them enlarged so they will be easier to reference when you are sculpting.
Roll pieces of polymer clay out on a clean table with a rolling pin and stack each sheet of clay between pieces of paper. Place a heavy book on top of the stack of paper and clay and leave it there for two to three days. This is called "leeching" and will cause the polymer clay to harden for better molding.
Roll up some aluminum foil and make a base by pressing the bottom onto a cookie sheet. Cover this base with a 1/2 inch layer of clay. Form an elongated wad for the base of the neck and head itself, which should be rounder and twice as long as the neck. The base for the neck and head should only add up to about 8 inches.
Add a 1/4 inch layer of clay all over the base of the neck and head. Look at the pictures you took from straight-on and both sides to study the nose. Form the general shape of their nose and place it 2/3 of the way down from the top of the head. Smooth the "seams"; add clay as you need it to finish their nose.
Add more clay to form the "eye sockets" at the middle of the face by making indentations, right above either side of the nose. Roll two small balls and elongate them on either side. Stick them in the eye sockets and form the eyelids around them.
Add clay to form the shape of the brow bones and forehead. Every lump of clay and every curve will add to the likeness of the person you are sculpting, so make sure you match it up the the pictures the best you can. Work slowly. Look back at your pictures and add small bits of clay at a time to form the cheeks.
Roll pieces of clay and the lips. Attach them to the face so that the opening of the mouth is about half-way between the tip of the chin and the bottom of the nose. Add more lumps of clay; and shape and smooth out the seams to get the chin and surrounding area of the mouth. Attach and shape the ears so the tops line up with the top of the eyes. Carve small details such as eyebrows, eyelashes and hair with the tip of a pencil or other fine-tipped object.
Preheat the oven at the temperature needed for your brand of polymer clay and place the cookie sheet with the clay bust on it on the bottom rack of your conventional oven. Bake at the time indicated on your package of clay. When it is done baking, carefully remove it from the oven with an oven mitt and let it cool.