First find the triangle placement for your eye and mouth features using colored ball headed pins. An isosceles triangle gives a younger appearance. The eyes should fall directly onto the eye line where your string is tied underneath the skin tone knit. The mouth should be 1/2 way between the neck and the eye line.
You need about 22" of floss for a pair of eyes on a 16" Waldorf doll head. You split the floss into 2 sections of 3 strands each. Run each section through beeswax a few times and then thread onto your 5" long doll sculpting needle. Remove the first eye placement pin and pass the needle through this place going from the front where your first eye pin was located to the back of the head, leaving the long strand in the front and tying off in the back. Rethread the floss that is left in the front onto a small embroidery needle. I like to make several vertical stitches about 1/8-3/16" where the eye will be, before I start my horizontal satin stitches, shaping the eye into a round or oval, or into a crescent shape for Asian or very smiling, crinkly type eyes- I do not find square eyes appealing, but some people do. I find that if I count my stitches, it is easier to match the second eye to the first. Once you are happy and done with the first eye rethread the floss onto the long sculpting needle and pass back to the back of the hear and tie off. The repeat with the 2nd section of floss for the second eye.
The mouth is done with the complete set of 6 strands of floss and I find about 18" is sufficient to embroider a sweet smile. I wax the floss and thread the large sculpting needle again, passing from front to back, leaving the long strand in the front and tying off in the back of the head. I make this first pass 1/4" to the left of the mouth placement pin. Then rethread onto the small embroidery needle and make a stitch 1/4" to the right side of the mouth placement pin, which I now remove. I then make another stitch, slightly smaller than the first just inside of the first, to make the bottom lip, rethreading onto the large needle and passing the floss through to the back of the head on the last part of the mouth stitch, and tie off. HTH.