Use Correct Lighting:
Use a photo taken in natural light, or with a remote flash. Standard camera flashes flood the flace with flat light that is hard to model. Having your sitter in in angled light lets you model the face in three dimensions.
Get the Basic Proportions Right:
If you are using a photograph, try tracing some points to give you 'signposts' to work with. It isn't cheating, its just a tool. Use negative space shapes to help you judge the relationships between things. If drawing from life, use the 'thumb-and-pencil' method to check face proportions.
Checking Key Points
Use negtive space to check the shapes between the features. Imagine a line straight down the model's face, through the pupil. Does the corner of the lip sit to the left or the right of it?
- The tilt of the eyes is correct
- the nose is wide enough and long enough
- the lips are the right thickness or thinness
- the jawline is the correct shape
- the hairline is the right height above the eyes
Look at the Little Things
When you are drawing a portrait, tiny differences can really change the way the face looks. So check the small things. Little stuff, like the way the line at the corner of the mouth tips down, the length of a dimple, the shape of the crinkles near the eyes - these things mark out an individual.
Often a portrait artist will slightly exaggerate features to emphasise them. Don't overdo it, or you'll end up with a caricature. But you can accentuate the size of the nose, the heaviness of the eyes or the fullness of the lips, ever so slightly. Step back from your model, and consider how you would describe them - not worrying about nice manners. Is the hairline receeding? Does he have a big nose? Does she have thin eyebrows?
Don't forget the hair
Lastly, make sure you pay attention to the hair. Hair tells us a lot about a person and can really change how someone looks. Learn to draw hairIt can dominate a picture and deserves as much attention as the rest of the image.