When I began this illustration I didn't really think about what to draw. I simply started by building up the light in what seemed to be a sensible order. I did, however, need to concentrate at this point as it was my aim to establish the forehead, cheekbones, jaw and anywhere else that might catch the light (Fig.01).
I continued to add to the areas that reflected light and defined the image according to my understanding of women's faces. I find that it is easier to keep things clean without the specific features being involved (Fig.02).
This is the first point where I started to detail any of the facial features. I usually deal with these whilst the image still has a hazy effect (Fig.03).
I then reduced the size of the brush to help me start doing the detail. It is important to pay attention to the expression of the eyes and mouth. I was trying to make the face look calm (Fig.04).
In Fig.05 you can see that I was now happy with the look of the face and started to move onto the rest of the detail. You can notice that I opened the mouth as I thought that it went better with the slightly hazy eyes. I also added some highlights to the eyes. To make the subject of your image seem soft and mellow, a good technique is to limit the impact of the bones - in particularly the cheek bones.
I then started to add more layers to start working on the hair and other features in the image. From this point I was able to revisit all of the layers and develop the most suitable feelings to portray on the face. When I was totally satisfied I merged the layers so I only had one layer for the face, one for the hair and one for everything else in the scene (Fig.06).
One I had finished and was satisfied with the base layers it was time to move on to the color. Firstly I added a layer over the image and then added further colors to select areas (Fig.07). If you were then to turn the layer mode to Color you would get something along these lines. The Color layer can get a little messy, which is an obvious drawback so I would suggest changing the blending mode to Overlay and adjusting it until you are happy.