Let's consider purely technical details of icon making
1. Lines, slopes
One of the most important parts of the image is the framework of the object, i.e. rough linear marking, which separates the object from the background. When creating large-scale images, the designer occasionally thinks about defining objects with complementary outlines. This is unnecessary because of the scale: even low contrast objects do not blur into a single whole. Icon graphics is different. Two solutions are possible: either object and background colors must be from opposite sides of the color chart, or the foreground should be divided from the background by contrast lines and shadows. I would like to discuss lines in more detail.
If we think again to the big-size images, we can note that in order to highlight edges, we can use any (including the most complicated) angles, Bezier splines and edges. Anyway, the line will appear ideal due to anti-aliasing. When decreasing the image scale to the size of an icon, situation changes greatly. When each single pixel is vitally important and can change the whole look of the icon, anti-aliasing is just unreasonable. It means that you have to consider the possible line angles.
The slope you choose for the line, determines the step for this line. Because each line consists of basic elements, the union of which defines its accuracy and visual appeal.
For example, a 18-degree angle consists of many small 3-pixel lines connected using a 1-pixel downshift:
This is how almost each line looks like. Basic element followed by joining and another basic element. Unfortunately, not each angle makes the line look attractive and not annoying.
For example, here are 25 and 20-degree angles:
It can be easily known which line is more attractive. The 25-degree slope makes a line consisting of equal 2-pixel basic elements. The 20-degree slope has a basic element containing of three lines: 3-pixel, 3-pixel and 2-pixel. The slope is more complicated, therefore, if not supported by additional visual effects, it brings a feeling of untidiness: the primary elements have contrast which is too obvious to hide from the human eye.
Now we can come to the first rule. The most "correct" angles must make as plain primary elements as they can. Thus, the perfect angles are 0 and 90 degrees. In them, 1-pixel basic elements are combined without downshift and form smooth lines. Less perfect are angles which form basic elements of 1, 2, 3 pixel with 1-pixel downshift. Surely, the lines will not be smooth, but the human sight will process the image and provide to the user what you intended to show to him. Also, the mentioned angles can be considered correct (but at a stretch): slopes with basic elements made of different lines shifted by more than 1 pixel.
It is the time to touch another issue. In the previous paragraph, I intentionally defined angles with primary elements of 1, 2 and 3 pixels as correct. Such small lines, especially when a large amount of them is joined, appear as a single whole. But what do we see if we change the basic elements to 10 or 20 pixels?
Here is an example:
It can be clearly seen that the line doesn't have solidness. It is not a single line anymore; it is a combination of different lines, situated near one another. Hardly any designer wants its composition to look that way. Thus, we come to another conclusion: if you use small angles, which make long primary elements, it must be reasoned and employed with great attention.
And, finally, the last thing I wanted to tell about lines. I already wrote that the basic element has to be as plain as possible.
For instance, a 25-degree angle can be drawn in the two (of course more of them exists) following ways:
In the first case the primary element is a 2-pixel line. In the second case, it consists of three lines: 3-pixel, 2-pixel and 1-pixel. The same slope but the image is different. The complex primary element produced the line messy.
This examples can be produced for almost any angle, so in your works, try to simplify as much as possible.
It can be stated without an overstatement that the color is the leading element of your work; not suiting or badly balanced colors can kill even the best idea. What can we write about the color in miniature graphics?
First, there is a clear rule: if the image looks poor when reduced to grayscale, it means the colors that were used are wrong. This rule is true not exclusively for icons but for the entire graphic design.
Second, you will probably unable to apply common RGB. Of course, you may use GIF colors only, but this ties you hand and foot. Gradients, shadows, dithering and many other tricks will not be available to you.
Third, try to increase the portion of "flat" color. The more consistently colored areas without blurring and jumps your picture has, the more neat it looks. Icons are too small and the excess usage of special effects makes the image look dirty.
Fourth, gradients. This is a great tool which can change the appearance of any project. Besides visuals, gradients are an ideal way to abolish the "broken line" look (lines with too long basic elements). But be careful when applying them since too many gradients can ruin the plain color, and be unable to fit into the gif palette.
Fifth, shadows and highlights. All rules for applying shades and flares in icon creation are totally identical to the rules of the general graphic design. The only thing I have to mention: create everything by hand. Don't use effects, make all shades and highlights in a separate layer and after that edit the opacity. When applying filters, you rarely can predict what the result will be. It is unfavorable when you don't control the process of creating of a project. It is awful if you don't control it when drawing miniatures.
And, lastly, sixth. Tinting is the main detail of pictogram creation, which greatly results the visual look of the composition. If the blue human eye in the icon is sized 1 pixel, increase the color intensiveness. For example, instead of 0, 131, 159 make 71, 195, 242. It doesn't matter that the human eye can't have this color; in the first example it will appear like a gray dot, and in the second example it will definitely be a blue eye.
Thoroughly control the image, do not allow the visual tricks to ruin your design. It is OK if something is not perfect from the technical point of view, but the entire picture must be perfect.
As an example, I drew the pack of juice standing before me. The image has plain color, gradients with broken lines, shades and flares and nuances.
If I wrote about something bigger than pictogram design, this part wouldn't fit into a whole book, but the resolution of compositions restricts fonts too.
The resolution of letters becomes the main issue as opposed to their beauty. Almost in all cases, unless the letters are the primary part of the image, the text size must be decreased to the greatest extent possible.
In principle, virtually any graphic studio has its own font with tiny characters. This font can be created in several hours. You can search the web and collect your own collection of very interesting fonts. First of all, I advice you to download the DS Pixel and Seventen 7Vedi website and the whole series of fonts from the Lakmus Lab website.
If you don't want a new font, little sizes of Arial and Verdana may work. As a last resort, you can draw the necessary letters yourself.
There are not many rules there. First, characters cannot be less than 5 pixels high or less than 3 pixels wide.
Second, letters should not use anti-aliasing. It transforms the text into an incomprehensible set of pixels.
Though, there are no rules without exceptions and the 5-point Arial looks rather understandable.