Let's consider strictly technical aspects of icon design
1. Lines, angles
One of the vital parts of the composition is the outline of the object, i.e. solid line, which limits the object from the rest of the image. When working with normal-sized graphics, the designer occasionally thinks about defining objects with additional lines. This is not needed because of the scale: even low contrast objects do not blend into a single whole. Pixel graphics is other story. Two variants are possible: either foreground and background colors have to be from opposite sides of the color chart, or the foreground must be separated from the background by visible lines and shadows. I will dwell on lines deeper.
If we return more to the big-size graphics, we can note that in order to define contours, we can use all (including the most complicated) angles, Bezier splines and edges. In any case, the line will appear perfect thanks to anti-aliasing. When shrinking the graphic scale to the size of an icon, situation changes greatly. When every particular pixel is equally important and can ruin the overall look of the icon, anti-aliasing is just not applicable. It comes that you have to think about the possible line slopes.
The angle you select for the line, determines the step of this line. Because every line is made of basic elements, the combination of which defines its neatness and esthetics.
For example, a 18-degree angle contains many tiny 3-pixel lines connected using a 1-pixel downshift:
This is how almost every line looks like. Primary element followed by joining followed by second primary element. However, not each slope makes the line look attractive and not annoying.
For example, look at 25 and 20-degree slopes:
It can be easily known which line is more appealing. The 25-degree angle produses a line consisting of equal 2-pixel basic elements. The 20-degree slope has a primary element consisting of three lines: 3-pixel, 3-pixel and 2-pixel. The slope is more complex, thus, when not combined by other visual effects, it brings a feeling of messiness: the primary elements have contrast which is too strong to hide from the human sight.
Here we can see the first rule. The most "correct" angles must make as plain basic elements as they can. therefore, the ideal angles are 0 and 90 degrees. In them, 1-pixel basic elements are joined without any shift and produce smooth lines. Less ideal are slopes which form primary elements of 1, 2, 3 pixel with 1-pixel downshift. Surely, the lines can not be even, but the human brain will process the picture and present to the viewer 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 touch another issue. In the previous paragraph, I intentionally defined angles with basic elements of 1, 2 and 3 pixels as acceptable. Such small lines, especially when a large amount of them is joined, look like solid. But what happens if we increase the basic elements to 10 or 20 pixels?
Here is an example:
It can be clearly seen that the line loses its solidness. It is not a single line anymore; it is a combination of several lines, located near one another. Hardly any designer wants its creation to look that way. So, we come to another conclusion: if you use small slopes, which produse long primary elements, it must be reasoned and employed with maximum caution.
And, finally, the third thing I have to mention about lines. I already wrote that the basic element should be as plain as possible.
For instance, a 25-degree slope can be produced in the two (sure more of them are possible) following ways:
In the first picture the primary element is a 2-pixel line. In the second picture, it consists of three elements: 3-pixel, 2-pixel and 1-pixel. The same angle but the look is different. The complex primary element made the line messy.
Such examples can be made for almost any slope, so in your works, try to simplify everything.
It can be stated without an overstatement that the color is the leading element of your work; improper or poorly balanced colors can ruin 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 converted to monochrome, it means the colors that were selected are incorrect. This rule is true not only for icons but for the entire graphic design.
Second, you will be unable to apply common RGB. Of course, you may select internet colors only, but this ties you hand and foot. Gradients, shadows, blending and many other effects will not be accessible to you.
Third, try to increase the portion of "flat" color. The more evenly colored parts without diffusion and jumps your picture has, the more clear it appears. Pictograms are too tiny and the over usage of special filters makes the picture look messy.
Fourth, gradients. This is a wonderful tool which can improve the look of any composition. Other than esthetics, gradients are an ideal way to abolish the "broken line" effect (lines with too long basic elements). But be attentive when applying them since too many gradients can ruin the flat color, and be not suitable for the gif palette.
Fifth, shadows and flares. All rules for using shadows and flares in icon design are totally the same to the rules of the overall graphic design. The only ine I have to mention: draw everything by hand. Don't use filters, make all shades and highlights in a separate layer and after that edit the opacity. If applying filters, you rarely know what the result will be. It is unfavorable when you can't control the making of a composition. It is worse if you don't control it when creating icons.
And, lastly, sixth. Tinting is the main aspect of pictogram creation, which largely results the visual look of the composition. If the green human eye in the icon is sized 1 pixel, increase the color intensiveness. 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 look like a gray dot, and in the second example it will definitely be a green eye.
completely control the picture, do not allow the optical tricks to ruin your work. It is OK if objects is not consistent technically, but the entire image must be perfect.
As an example, I pictured the packet of juice standing in front of me. The image has plain color, gradients with broken lines, shades and flares and tints.
If I talked about something bigger than icon design, this chapter wouldn't fit into an entire book, but the resolution of compositions restricts fonts too.
The resolution of letters is the leading aspect as opposed to their fineness. Nearly in all cases, unless the letters are the main part of the project, the text size must be reduced to the largest extent possible.
In general, almost any design studio has its own font with small letters. Such a font can be crafted in several hours. You can browse the internet and make your own collection of very nice fonts. Primarily, I would recommend you to get the DS Pixel and Seventen 7Vedi website as well as the whole series of fonts from the Lakmus Lab website.
If you don't need a new font, small typesizes of Arial and Verdana may work. As a last resort, you can draw the necessary characters by hand.
There are quite a few rules there. First, characters cannot be less than 5 pixels high or less than 3 pixels wide.
Second, letters cannot use anti-aliasing. It transforms the font into an incomprehensible set of pixels.
However, there are no rules without exceptions and the 5-point Arial appears rather readable.