To do the lightest parts of the skin, don’t just leave the part black. There are no perfect white pars on a work other than a highlight. Even then, some of the highlights can sometimes be not fully while. Try not to use an eraser to lighten the parts after going dark. First work up in layers until you get your desired value. Should it be way too light, then refer to using the eraser, but only use in emergencies, an if you’re going slow, this shouldn’t be too much to worry about... the reason i say this s because i have found that erasing never seems to leave the part you erased the same. I alters how the graphite interacts with page.
To draw lips there are many different ways. To my immediate right, is a crop of one of David Kassan’s drawings, and bottom right is Armin Mersmann’s. Both done very differently. Kassan has blended them in to make them appear much softer, and once again, sometimes less is more in terms of details. Both are women’s lips, maybe Armins being slightly less flattering. However something you notice on both... there are no lines. They haven’t drawn any lines to show wrinkles. They have rendered them in and felt the surface. That is something many people fall into the trap of... they se a wrinkle and draw it as a line, however its not a line at all, its where light doesn’t hit. If the light is coming from above, as in these two, the upper lip will cast a shadow over the inner part of the lower lip, and once again a shadow more subtle on the lower part of the lip, which curls around an faces away from the light. Studying light falling on a sphere will really help yur understating on this.