"The Making of a Kiss" post showed my process, but it wasn't actually a tutorial for how it's done, not to mention that the medium, chalk pastels, is a bitch for anyone starting out. So I've put together an ACTUAL tutorial for a basic sketch here, at the request of
Step 1. Block out your shapes
First and foremost, make sure you have good lighting, a flat surface, some extra pieces of paper (I use ordinary printer paper), a clean eraser on your pencil (rub it against your jeans if there's black gunk on it) your pencil, a sharpener, and your crayons. If you're really, really confident in what you're doing and your knowledge of anatomy, you can work from your imagination, but if you're that confident, you're probably not reading this, so GET A REFERENCE PICTURE. There's no shame in this. Everyone uses them when it's tricky or they have to be precise about a likeness. It doesn't make you a bad artist, indeed, it makes you a much better one. So decide who you want to draw and google or freeze-frame until you have the picture that you want.
It doesn't have to be exact. Feel free to use the hair from one picture, the clothing from another, the face from a third, the body position from a fourth, or to change things in the single picture that you do have. If you look at the entry for the "Sluagh" coverart, you'll see an example of an experienced artist using reference pictures. Can you see what I did with them? Sure. I used them for angles, feature proportions, feature placement, etc. But I tightened the brows and dipped the corners of the mouths to change the expressions, altered the lighting, added scars and tattoos, increased the prominence of bone structure to indicate age and a general hardening, changed the clothing, and changed the hair. But there's no way, as often as I've looked at it and even drawn it, that I could reproduce the exact shape and proportions of Matt Lewis' nose when his head is ducked a little and looking slightly to the left without at least some kind of reference pic.
What you want to do here is just place circles, cylinders, and other basic geometric shapes that will form the building blocks of the person or people you are drawing. A standard jointed wooden artist's model is a great help here until you get the hang of it, and there are a billion different sites and books that can help you with this part as well. Keep drawing and re-drawing this part until it looks right, but keep your lines relatively light, because you will be erasing them. It can help to put lines down the center of the 'face' and across the 'eyes' to help you get a sense of where the head is pointing, and if you're drawing more than the face and shoulders, generally start with the head and the line of the spine.
Drawing the body, especially in complicated positions like action and romance is a bitch. The rules of perspective, foreshortening, the way the body twists and flexes...honestly, if you're just starting out, stick to faces. It's so much easier, and it will help you develop general confidence in your work before you start trying to keep the proportions correct on an arm pointing straight at the viewer or bent up behind a person to brace them while they twist to lick their partner's neck.
I use a mechanical pencil for this because the line is even and consistent, and it also erases more cleanly than a standard #2.
By the end of this step, even though there'll be no sense of WHO the picture is of, WHAT it is of should be pretty obvious. In this case, it's a simple portrait of a young man (a woman's jaw would be more tapered, an older man's head more blocky with a thicker neck, and a child's head rounder with a shorter jaw) looking in 3/4 view towards the viewer. You should be able to tell this at a glance (it's a man and a woman kissing, it's a child crying on their knees, it's a young woman dancing, it's an old man sitting at a desk with his head in his hands, etc.) or you need to keep re-working it until you can. This is the skeleton of your sketch, and if the 'story' you're trying to tell isn't here, it won't be there in the end.
Step 2: Your outline sketch
This may seem like the most intimidating step, but it's really not so hard when you're building on a good foundation.
Start, oddly enough, with the hair. It's the simplest thing to build off of the skull, because no matter if the person is fat, thin, muscular, ugly, beautiful, old, young, or whatever, the shape of the skull itself is pretty much the same, and hair will help create a frame for your face and tell you how much of it is actually showing. Sketch it out lightly, using sweeping, feathery pencil strokes. Use reference pictures if you need to for a particularly difficult hairstyle, but don't worry about the color or anything really exact for now. You're just creating an outline, almost a sillouhette. Once that's set, erase the line of the skull underneath.
Now using the remaining portion of the framework you created in the first step, establish the jawline, the placement of the ear (whatever, if any of it, shows beneath the hair is just being placed for now. Don't worry about all those swirly parts, something that looks like the letter G is actually fine for now. When you're going up the side of the face, use that eye-line to place the dip of the eye socket and the rises of the cheekbone, mouth, and chin in a 3/4 like this.
Go down the neck. As with the jawline, this is really easy on most characters who are reasonably fit, and it will be almost following the lines you set out in the first part exactly. However, if you have someone like Slughorn or Uncle Vernon who's a bit...um, generously fleshed, you will want to use the first step as a reference and sort of 'hang' the visible jawline, neck, and chin(s) as appropriate.
Collarline and clothing. Take some time to look through a parochial school yearbook, some lawyer's websites, and some men's fashion magazines. This is vital research if you want to become an HP fan artist. Why? Because dress shirts, their collars, and ties (tight, loose, untied and draped, etc) are going to be in almost every picture of a Hogwarts student. Get to know them, get to love them, get to be able to draw them in your sleep and know how they hang from every angle, and if you're not sure, find a reference picture. Also, do the same with dress slacks, belts, cardigan sweaters, sweater vests, graduation robes (the best match to the cut of the Hogwarts robes) knee-length pleated skirts, knee socks, men's dress shoes, and women's oxford shoes. Be warned in advance that the layering and draping of these is hell. Learn to live with it, pick another fandom, or only draw them naked/in Muggle attire...but if you don't want to wildly limit yourself, I suggest the former.
The features...now now, stop crying. It's not that bad, really.
The trick here is that you're never, ever drawing a human face or an expression. Yeah, I know, it sounds crazy. But it's a lot easier that way. What you're doing is drawing lines, shapes, and blocks of color/shade. That's all it ever is, and it's a lot less intimidating than drawing people if you reduce them to what they actually are. Start at the top of the face where you've already set the eyeline and framed with your hair and work your way down, sketching out the following (off your reference picture until you're really confident):
Eyebrows - two sketchy lines showing only the general arc of them. Pay attention to the point where the brows meet the nose in particular, because here's where a huge amount of human expression is contained. Up, down, pinched in, drawn apart...check your reference pic and make funny faces in the mirror while staring at your eyebrows. Believe it or not, more than anything else, these two lines will give your sketch a sense of emotion. But they are just lines, so look at them only as arcs and angles and compare them to the arcs and angles you're trying to show. Rule of thumb: Eyebrows will align with the tops of the ears and the inner corner of them will align with the nostrils.
Eyes - Unless your character is Asian, there is a crease where the lid folds. Draw that line first, then the upper lash-line, then the lower lid, the inner corner, and the under-eye crease. Reduce these to simple lines and don't worry about detail yet. Now use semi-circles to place the iris and pupil. Don't close these lines, but leave them open for your highlight. Rule of thumb: The outer edge of the mouth will align about one-third of the way into the eye. The whole circle of the iris rarely shows. Men's eyes are smaller than women's eyes which are smaller than children's eyes. The larger the eye, the more helpless the character will look.
Nose - Bridge line, shape of nostrils, shape of nares (the flared part over the nostril). That's it. And be aware that the bridge of the nose is never, ever a truly straight line. Noses are also the number-one facial ethnic differential. If you want your character to have a 'look' (Slavic, Aryan, Asian, African, Indian, Celtic, Semitic, Gallic, etc.) make sure to match the shape of the nose carefully to someone actually of that ethnic group. In this case, Zach's nose is very classically Anglo-Saxon, underlining cesaretech's universe in which his family are long-standing British pureblood wizards. Rule of thumb: The bottom of the nose aligns with the bottom of the ear.
Mouth - The upper lip is a three-part structure...the plump middle portion with the 'cupid's bow' in the center and the two sides that taper down to the corner of the mouth. Pay attention to the general shape here, you'll be drawing it for everyone, but you'll only completely outline the lower lip in a woman or girl. For boys and men, you can give them the poutiest mouth you want, and it will never look feminine as long as you remember to only indicate it by drawing a slightly curved line to mark the bottom of the lower lip rather than drawing the whole thing. Another line just below that marks the top of the chin, and don't forget to indicate the dip of the philitrum between the mouth and nose, or your whole mouth area will look oddly flat. Rule of thumb: The width of the cupid's bow is the same as the distance between the nostrils.
Part 3 - Base color
I increased the saturation on this scan so you could see it clearly, but you actually want to do this part rather lightly (better sense of the true tones can be seen in the last image). Lay down anywhere that has a solid block of base color...flesh, colored clothing, hair, etc. You are putting down the LIGHTEST COLOR. Apricot for Caucasian skin, a very, very light layer of red-orange or yellow-orange for other ethnicities. All blonde, red, or brown hair will start out with dandelion as the base color. True black starts out with cerulean. White and gray remain uncolored in this step. Increasing the contrast made it seem blotchy, but you want a smooth, even 'base coat' here, making no attempt at shadows or shading.
Establish your eye color, and use carnation pink for your lips (unless it's someone wearing lipstick, in which case use the lightest shade of the appropriate color, whether that's a light layer of true red or for something more gothic, a layer of cerulean for what will be black), leaving a white space at the fullest part of the lower lip. The exception to this is if you want a look of really, really severe sickly pallor, in which case you match the lips to the skin tone, or if you want the person to appear to be dead or severely hypothermic, in which case you use violet as your undertone.
Step 3 - Shading and shaping
This picture has also been upped in contrast so that you can more easily see what I'm talking about.
What can often seem one of the most difficult steps is actually the easiest. Start with shading white clothing in cerulean, colored clothing in the one-shade-darker crayon as appropriate (if the clothing is black, your base color should have been cerulean, so now you can switch to gray), and lightly suggesting where the darkest parts of the hair will be with a few lines of brown. Now shade the skin using brown.
This is not so difficult, as I promised. Just break it down into Light shade, Medium shade, and Dark shade, and use light, medium, or heavy pressure on the crayon. See the blue lines on the picture above? That's how you're going to do it. Not by drawing blue boxes on your picture, of course, but by turning the shadows into shapes. It's not the bridge of his nose, it's a triangle-shaped dark shade. It's not the bottom eyelid and dip of the eye socket, it's a diamond-shaped medium shade. It's not his lower lip or the top of his cheekbone, it's two quadrangles of light shade.
Until you can spot this immediately on your own, go ahead, print out your reference picture or make a copy of it, and use a pen or your pencil to actually outline the different shapes of the shading like on this picture. Then it's a piece of cake, because after all, while you might not be able to get the perfect shadow on a nose, you can damn well draw a triangle and color it in pretty darkly, right?
Step 5 - Finishing it off
Using a well sharpened black crayon, go over all the lines from step 2. Color anything that is actually black, like the stripes of the Hufflepuff tie and the pupils of the eyes. Use the side of the crayon's conical tip to gently deepen the darkest shadows from the previous step.
Color and texture the hair. Use long, sweeping strokes to make your lines form the hair's individual strands. Remember that brows are a few shades darker than hair color. Use black for eyelashes unless it's a red-head, in which case use brown. Black is always your deep-shade color on hair. Only the base and mid-tone colors vary, and those are as follows:
Flaxen blonde (Draco) - White base, yellow mid-tone
Blonde (Zach in this picture) - Dandelion base, brown mid-tone
Red (any Weasley) - Dandelion base, orange, red-orange, and brown mid-tones
Brown (Hermione) - Dandelion base, lots of brown for the mid-tone
Black (Harry) - Brown base, black mid-tones
True Black (Snape, the Patil twins) - Cerulean base, black mid-tones
White (Xenophilius) - White base, cerulean mid-tones
Grey (Dumbledore) - White base, gray and cerulean mid-tones
Pink, Purple, Blue, Green (Tonks or Teddy) - Carnation pink/red-violet, red-violet/violet, blue-green/cerulean/indigo, yellow-green/green/blue-green
Slightly deepen the iris color on the upper portion of the iris on the side away from the highlight.
If applicable, use brown for freckles and carnation pink for flushed cheeks. If there is colored eyeshadow, do that now.
And.....
Congratulations! You're done!