1. First the sketch. Now you have to be able to draw a face in the first places. Eyes should be in the middle of the head, many tend to draw them too high. The space between the eyes, nose, lips and the end of the face are about equal. Don't forget the ears! Think if the hair as big shapes instead of strands, it makes it a lot easier to sketch then. Make a couple of bigger sections of hair. Make rough shading, marking the major shadows.

* It's a lot harder to sketch with a Wacom than with real pen and paper, but then you can have it on a seperate transparent layer. Do as you want.

* A general tip that always applies: zoom in to draw details and zoom out to look at proportions and shades, do it VERY often!

2. Now you can either put the sketch as the top layer or use Multiply layers (depending on if you have used a transparent layer). Have the background as the bottom layer, and think of what you want in the background because this might affect your shading later. Draw the basic colour and shape of everything to have a clear view of how it will be. Recommended seperate layers, in this order with hair as the top layer:
* hair
* face
* clothes and other things.
* neck / bust

Lock the layer opacity to keep the shapes intact, except for the hair.

4. Begin adding features such as eyes, eyebrows, nose and lips. Draw the eyes, eyebrows and lips in a seperate layer (see other tutorials). The eyebrows should be done about the same ways as hair (tutorial) but a lot simpler of course. Shade the face and ears even more. Try using the brush as much as possible for now, and not the burn/dodge tools. Add a couple of different shades and colours, e.g. some part of the face are redder.

8. Add the background. In a portrait you want to focus on the face, but the background could be very detailed too, just not in this example. If you'd like to you could add additional coloured shading to make it more alive (see screenshot). Have them on a seperate layer in case you change your mind. To have more intense colours you can finalize by flattening the pic and adjusting brightness/contrast.

You can always alter the shading according to your taste, as long as it looks good. You don't have to draw EXACTLY like the model. For example to accentuate a certain feature you can make stronger shading and vice versa. I almost always make eye a lot lighter than they are because it looks good. The hair is impossible to draw exactly like it is, but you can make up some so it looks good.