When liquefying, adjust the brush pressure as needed, generally about 50. This requires skill, and slow practice can make the picture reach a natural thin face and waist.
The second way: there is another stupid way. Tick off the selection and cut off all the unnecessary parts, such as fat arm roots, lifebuoy-like meat on the waist and protruding cheeks. The steps are as follows.
1. Draw the ideal shape with pen drawing first, and of course don't tick off the unwanted parts.
2. Use shift+ctrl+I to select the dashed line in reverse, and then "delete" the unnecessary part, and then start thinning.
3. Invert the dotted line shift+ctrl+I to feather twice (so that we will be more natural in the complementary color later).
4. Draw the face with the color of the face and the arm with the color of the arm, but there are some differences. For accuracy, you can use the pipette tool. If you are coloring clothes, you can suck the color of clothes.
In this way, we basically completed the complementary color, and then continue to refine. Of course, if we are lazy and don't want to draw, we can make do with it.