Before getting started, one must determine which type of colour toned person he/she should be painting. Native American people have different type of skin, African people have different while Asian and Arabic have a different complexion, though, they all have dark toned skin. Once you have decided, use the World Wide Web to search all the types of people of that specific category. Determine closely all the images, and see their skin texture. Watch closely their facial attributes, as learning about these things will eventually help you painting a close to perfect portrait.
After all the research, you should start preparing to paint the portrait. Choose three to four basic colours through which you will be able to make up the rest of the tones. It is recommended that one chooses a light, a medium and a darker tone. Prepare your canvas, and assemble your pencils, paint brushes and colours alongside it.
Once you are fully equipped, start sketching the model or image on the canvas. Once you have finished sketching the basic facial attributes, eyes, nose, lips, hairs, forehead, ears, neck and eyebrows, you should apply all the main colours according to the picture. Whole face along with neck should be painted with the base colour while the eyebrows and the hairs should be painted with a further darker colour to shape up the portrait a bit.
After applying all the base colours, you should start refining out the colours and textures of the face. It will shape up the entire face to a more recognisable form.
After you have finished refining your portrait, the most important part of painting comes in, the final touches. These final touches further refine your portrait, and will determine how your end product looks like after you have finished.