Have your easle off to your dominate and level with the model. The goal is to have your head and eyes shift very little from model to canvas. Stand, don't sit this will allow greater movement of your body and arms to work faster and better.
Take your hand with the brush and make a thinned out line with paint (always draw a portrait in the medium that you are going to finish with, otherwise the outline may bleed through. Here in my example I used charcole, it is a bit more of a challenge that's why I use it.) Avoid using strong black as you will not be able to eliminate all the lines and cannot redraw as easily. Stretch your arm out to the fullest extent and with your brush handle find the uppermost point on top of the model. Could be a wave of hair or the top of the skull if they are bald. Make a small slash or mark on the canvas where you want the top of the subject to reach.
Swing your arm back to the model and measure the angle from that top point to the outter most part of the left ear (as you see it, their right ear) without lowering or changing your out stretched arm and without changing the angle of the brush handle swing back to the canvas and make a small mark like the first at the point of the outter ear. On the canvas you should have two small marks, one for the top of the head and the ear.
Now stretch out the arm and measure the distance and angle from the ear point to the bottom of the nose. Make another mark on the canvas where the nose is located in relation to the ear and top point of the head. From these three points the entire subject can easily be captured and put down in proportion on the canvas!
From the ear point measure out with the handle of the brush and with your arm straight out find the angle and distance of the inside of the nose by the eye. Make a mark on the canvas. Then find the SAME angle and distance from the nose to the point by the eye. With another mark you can make a small X and that is the EXACT point of the nose nearest the eye. Repeat for the point of the eyebrows, nostrils, mouth...every single point on the face.
With this system all the features mathmatically fall in, there is no eyeballing and judging distance lines and angles with out a careful measurement. Even curves of the jawline and subtle features like freckles and moles can quickly and easily be found with this meathod.
Once the outline of the subject is down then let it dry thoroughly. Next is shadows and tone of color. Leave the highlights for later. Quickly, I mean that, if you take too much time on the shadows you become dependant on the original outline...which may have been obliterated in places by the paint used to indicate shadows on the face. After a quick lay down of the tones go back and redraw the outline again. Using a slightly darker paint than the darkest shadow will allow you to replace lost lines and to find adjusted ones.
Then lay in the highlights. Start with the lightest one and move to the subtle lights near the lightest shadows. For shadows work from dark to lightest, for hightlights the opposite. Take a break and let your eyes adjust to what you really see as a whole of the subject rather than all these little marks now. !0 min later get back to it with another redraw. This time though try to be a little more sensitive to line weight and darkness. A really good portrait has no lines at all so when you redraw at this stage you will keep them light and very accurate.
Try to work in straight lines, little dashes that represent the faucets of a curve. Keep the brush and paint moving in the same direction of the forms so you have a volume effect that subtly speaks to the viewer. Keep your work fresh, don't tighten up too much and keep going back to that drawing until the subject can look at the painting and say wow! Because if the subject recognizes themselves (where possible) then you are most certainly going to have friends that know them recognize their likeness from your canvas and paint!
Make sure you can see color, there are blues and cools in the shadows, but not all. The colors that I use to achieve ANY skin tone are simply: Naples Yellow Hue light, Alizarin Crimison, Burnt Umber, Raw Sienna, Black, Ultra Marine Blue, White, Cadium Red Light and Yellow Ochre. Through these you can mix the tone of any portion of the face and place accurately!
Practice makes it easier, start with your own face in a mirror to practice with out bothering another model. Then when you can bang out your face easily then move to a live model. After years there then work from photos. Why so much time? To educate your mind as to how the flesh, muscle and bone work in concert for expression, mood and accuracy.
Lastly, the goal is to create a portrait that has great amounts of detail, accuracy and expressionistic mood. A portrait is just not entertaining if there is no emotion. Read the person, look at their eyes, brows and cheeks, how is the mouth set? These are indications of personality. Capturing personality in a portrait is the hardest but most rewarding part of portraits!
TATTOO TIPS FOR PORTRAITS:
When ever possible draw from life, if not trace out the easiest to see lines on a light table from a photo and then set the paper to the side of the photo and draw in what you couldn't see. Stencil in only the most obvious lines, middle of the mouth, corners of mouth, bottom of nose, size and position of nostrils, eyebrows, ears, hairline, chin line and eyes. And tattoo these lines at a blood line, or with very very light ink.
Next lay in the hair, back ground and all the other darkest shadows. You MUST get these down quickly and accurately as you can't go back and change later. Then I put in the lightest shadows with the thinnest ink and move to darker ones. Somewhere in the middle add brown ink to achieve a very detailed and rich skin tone in your tattoo.
Then touch up the darkest shadows and areas that need work for detail. Finally add pure white highlights on the nose, cheek and eyes. Keep them accurate and make certain that each highlight in the eye is the EXACT same shape and size and in the proper location as the other. If the highlights are off but everything else is right on then you will have a poor portrait, affect the expression or worse yet make the tattoo appear to have a lazy eye!
If you really want to show off, then add a touch of blue and red in places on the portrait where the cools and warms typically go. But do these very lightly, for instance with a single pass of a large magnum so there is very little ink placed over the color already down. This will achieve a glaze type of affect that one can achieve with paint. Try it, but go light and make sure that the color is of the same value as the shadow.