Let's consider purely technical details of icon making
1. Lines, angles
One of the vital elements of the image is the framework of the object, i.e. rough linear marking, which limits the object from the background. When working with large-scale images, the designer occasionally cares about defining objects with additional outlines. This is not needed because of the size: even low contrast objects do not blend into a one. Pixel graphics is different. Two variants are available: either foreground and background colors have to be from different sides of the color wheel, or the object must be divided from the background by contrast outlines and shadows. I would like to discuss lines deeper.
If we return again to the big-size graphics, we see that in order to highlight contours, we can use all (including the most complex) angles, Bezier splines and edges. Anyway, the line will appear ideal thanks to anti-aliasing. When decreasing the image dimensions to the size of an icon, situation changes dramatically. When each particular pixel is equally valuable and can change the overall appearance of the icon, anti-aliasing is simply not applicable. It comes that you should think about the possible line slopes.
The slope you select for the line, specifies the step of this line. Because each line is made of basic elements, the union of which defines its neatness and esthetics.
For instance, a 18-degree slope consists of many tiny 3-pixel lines connected using a 1-pixel downshift:
This is how almost every line looks like. Primary element followed by joining and second basic element. Unfortunately, not every slope makes the line look attractive and not annoying.
For example, look at 25 and 20-degree slopes:
It can be easily seen which line is more attractive. The 25-degree slope produses a line consisting of even 2-pixel primary elements. The 20-degree angle has a primary element containing of three lines: 3-pixel, 3-pixel and 2-pixel. The slope is more complicated, thus, if not supported by additional visual effects, it brings a feeling of untidiness: the basic elements have contrast which is too obvious to hide from the human eye.
Now we can see the first rule. The most "appropriate" angles must make as simple basic elements as they can. Thus, the ideal slopes are 0 and 90 degrees. In those, 1-pixel basic elements are joined without downshift and produce smooth lines. Less perfect are slopes which form basic elements of 1, 2, 3 pixel with 1-pixel downshift. Of course, the lines will not be smooth, but the human sight will process the picture and present to the user what you meant to show to him. Also, the mentioned slopes can be considered acceptable (but at a stretch): slopes with primary elements consisting of different lines shifted by more than 1 pixel.
Now we can discuss another issue. In the last paragraph, I intentionally defined slopes with basic elements of 1, 2 and 3 pixels as acceptable. Such small lines, especially when a great amount of them is joined, appear as solid. But what do we see if we change the basic elements to 10 or 20 pixels?
Here is an example:
It can be obviously noticed that the line loses its solidness. It is not a continuous line now; it is a set of several lines, situated near each other. Hardly any artist wants its creation to look inconsistent. Thus, we have another rule: if you use minimal angles, which make long primary elements, it has to be justified and employed with great attention.
And, finally, the third aspect I wanted to mention about lines. I already wrote that the primary element should be as plain as possible.
For instance, a 25-degree angle can be drawn in the two (sure more of them exists) following ways:
In the first picture the basic element is a 2-pixel line. In the second case, it is made of three elements: 3-pixel, 2-pixel and 1-pixel. The same angle but the image is different. The complex basic element produced the line untidy.
This examples can be made for about any angle, so in your projects, make sure to simplify as much as possible.
It can be said without an overstatement that the color is the leading element of your work; improper or poorly matched colors can ruin even the best idea. What can we say about the color in miniature graphics?
First, there is a clear rule: if the image looks bad when reduced to grayscale, it means the colors that were chosen are incorrect. This rule is true not only for icons but for the entire graphic design.
Second, you will be unable to apply safe RGB. Sure, you can use GIF colors only, but this limits you greatly. Gradients, shadows, blending and many other effects will not be accessible to you.
Third, try to increase the portion of "plain" color. The more evenly colored areas without diffusion and jumps your composition has, the more clear it looks. Pictograms are too small and the excess usage of special filters makes the image look messy.
Fourth, gradients. This is a great tool which can change the look of any picture. Other than esthetics, gradients are an ideal way to get rid of the "broken line" effect (lines with too long primary elements). But be attentive when applying them because too much gradients can kill the plain color, and be not suitable for the gif palette.
Fifth, shadows and flares. All rules for using shadows and highlights in icon creation are totally the same to the rules of the overall graphic design. The only ine I would like to note: create everything yourself. Don't apply filters, make all shadows and flares in a separate layer and then edit the opacity. When using effects, you rarely know what the result will be. It is bad when you can't control the process of creating of a composition. It is worse if you don't control it if creating icons.
And, lastly, sixth. Nuancing is the main aspect of icon creation, which greatly results the visual look of the composition. When the blue human eye in the icon has the size of 1 pixel, increase the color saturation. For instance, instead of 0, 131, 159 make 71, 195, 242. It doesn't matter that the human eye can't have such color; in the first example it will appear like a gray dot, and in the second example it will really be a blue eye.
Thoroughly control the picture, do not allow the visual tricks to spoil your work. It is acceptable if something is not perfect technically, but the whole image must be perfect.
As an example, I pictured the pack of juice standing in front of me. The picture has flat color, gradients with broken lines, shadows and highlights and nuances.
If I wrote about something bigger than pictogram creation, this chapter wouldn't fit into an entire book, but the resolution of pictures restricts fonts too.
The size of letters becomes the main issue as opposed to their beauty. Almost in any case, unless the letters are the primary part of the composition, the font size has to be decreased to the greatest extent possible.
In principle, almost any graphic studio has its exclusive font with little letters. Such a font can be crafted in a couple of hours. You can search the web and collect your own library of very nice fonts. First of all, I would recommend you to get the DS Pixel and Seventen 7Vedi website as well as the whole set of fonts from the Lakmus Lab website.
If you don't need a new font, small typesizes of Arial and Verdana will work. As a last option, you can draw the needed letters yourself.
There are quite a few rules there. First, letters cannot be less than 5 pixels high or less than 3 pixels wide.
Second, letters cannot use anti-aliasing. It transforms the text into an unrecognizable mixture of pixels.
Though, there are no rules without exceptions and the 5-point Arial looks perfectly readable.