New cleaned up version HERE
This thread is getting old now. Some of the links are not working anymore. I might put up a clean version of this tut somewhere, someday.
I'm working on a real tutorial for my website, but I wrote something short because people keep asking me too. I'm sure I forgot about a lot stuff but I think that I have covered the major things. If anyone wanna add or correct something please do!
1. What are you trying to draw? Your subject and composition should work on a fundamental level. If not, then no rendering in the world can save it. There's a lot to say about subject and composition but it's a too large subject for me to go into right now, but I can say that if you think "Oh ,I bet it will look better when I start coloring it" then you might be in trouble.
2. Painting/Rendering. Not as important as #1 since there are several ways/styles to do it. Rendering style is also a subject to personal preference but a few generic 'rules' must be considered. Below are a the most important things to keep in mind. Forget one and the painting will most likely look a bit odd, forget many and you'll have a disaster on your hands, unless you're into modern art.
Light color and ambient color (shadow)
What kinda enviroment is your subject in? On a summerday outside the light is yellow and the shadow is blue. Wintertime there's a lot of reflective light from the snow that kills shadows and flattens the rendering (no shadows). One of the most common newbie mistakes is that they render everything in their 'local color' and just add black the the shadow and white to the highlights. This leads me to the next point:
Everything is a 'lightsource', that's why we can see anything at all.
Try holding your palm (in light) close to different shadowed surfaces and watch what happens to the shadowed surface. Turns red? Shadows does not reflect as much light as lit surfaces.
In fact the entire sky-dome is a reflective lightsource, it grabs the sunlight, turns it blue, and sends it out in all sorts of directions. Since the sky is a 180 degree dome it can get to spots the sun can't get too, and that's why shadows are blue outdoors.
Learning how to do reflective light (radiosity) is one of those things that really upgrades your art.
Example: The leftmost fist gizmo that has some of the red color from the leg on it. The source of this light is the brighter part of the leg below.
Speculars are in the eye of the beholder (angle relative) and only occur on shiny/gloss/wet surfaces. Try painting the surface without the speculars and add them later with a brush on opacity. Outdoors the specular color is sky blue.
Highlights (very bright dots or patches) are often:
A) A light
B) Something wet that reflects a light, ie. a specular.
Example: Look on her black leather/plastic suit. The only light rendering you see on that is the speculars. Her breast color reflects on both the inner sides of the arms. I've picked a grey specular because it's pretty close to blue and I got some grey in the background and as an ambient color.
Sometimes edges between extreme light and shadow become saturated. On human skin the edge is often red-orange-yellow. If someone is sitting indoors or under a tree, and a spot of sunlight hits on the skin, the spot will most likely be bright yellow or white, and the shadow will be dark grey-purple or something not very saturated. The edge however, being close to midtone, will try to be as saturated as it can, and midtones can always be more saturated than brights and darks. Sometimes if you want something to be saturated you can try ta make the edges saturated and leave the shadows and lit areas as they are, cuz they will appear saturated cuz of the edge. This is often more effective than just smudging saturated shadows and lit areas. Smudged edges are boring. It's a good idea to keep the shadows less saturated than the lit area, so by making the edge saturated you can make the entire surface appear saturated.
Another example. On a white t-shirt outside a sunny day, the shadow will be blueish, and the lit surfaces white, but the edges will be yellow, not blue-white. This is because the lightsource is yellow, but with the t-shirt already being white it can not show anywhere but on the edges.
One more thing, bright yellow looks more intense than pure white (which looks cold).
Example: Look on the upper leftmost leg where the highlight meets the shadow. It's hard to spot but I put a bit of red into the shadow there.
Example 2: The back is obviously overexposed, so I made the edge yellow.
Really hard to do. You must either make a 3d model or be able to guess good (have a good 3d/shape sense). Shadows can really be your friend and add a lot of atmosphere to a painting, but don't put things in shadows cuz u cant paint that detail. It's like hiding the feet in high grass, and the head in a tree.
Shadows tend to get fuzzy the further away they stretch from the 'caster'.
Things further away have more skycolor in them and are as a result less contrasted.
Example: Look at the tail. The background is white, so the fog color is white too. This results in a flat grey color, because the fog aslo reduces saturation and contrast.
This takes a lot of practice to learn, especially with natural media. For example, when painting skin color you can use grey as a shadow color and it will appear blue, although it's not. The best way to deal with color relativity is to use a brush on opacity and blend colors that way. Mixing colors with the palette sliders is very hard.
Simplify and flatten! Really important! Texture is nice but random brushstrokes on a flat surface is not texture. Paint so it looks like a low geometry model, ie. keep the surfaces flat (or curved) and clean. Remove any strokes that does not stay within the value tolerance of the surface you're painting. With this I mean that you can not always go all the way to white or all the way to black. Mostly you aren't allowed to fully render all the rivets, cracks and neat little details you had in mind, because the light situation won't allow it, or because it would be distracting.
Texture adds a lot to a picture, but make sure that you get the raw surfaces right first. I sometimes add textures later with a textured brush.
Remove contrast, saturation, sharpness and highlights on unimportant details, especially near the image borders (or atleast try to make those details less interesting).
Reversed: put more contrast, saturation, sharpness and highlights on the objects you want the eye to look at.
Put more details on the important spots and less on the unimportant.
Faces are important spots, especially on portaits. Spend a lot of time on getting the faces right.
Example: Nobody has perfect skin. Learn how the hue varies between different parts of the body. A plain monotone body will look plastic. Frank Frazetta is a master at varying hues.
Example: Try not to wander of into extreme shadows or light when doing texture details.
How do you learn all this (and much more) you say? Answer: Thousands of studies! There is no other way. As you draw and paint your lines and stroke economy will improve too, and you'll develop a style.