Let's consider strictly technical aspects of icon creation
1. Lines, angles
One of the most important elements of the image is the framework of the object, i.e. solid linear marking, which limits the object from the rest of the image. When working with large-scale graphics, the designer occasionally cares about defining objects with additional lines. This is unnecessary because of the scale: even non-contrasted objects do not mix into a one. Icon graphics is different. Two solutions are available: either foreground and background colors must be from opposite 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 more to the big-size graphics, we see that in order to define edges, we can use any (even the most complex) angles, Bezier curves and borders. In any case, the line will appear perfect thanks to anti-aliasing. When shrinking the graphic dimensions to the size of an icon, situation changes dramatically. When each single pixel is vitally valuable and can ruin the overall look of the icon, anti-aliasing is just unreasonable. It comes that you have to consider the possible line slopes.
The angle you select for the line, specifies the step of this line. Because every line consists of primary elements, the union of which defines its accuracy and visual appeal.
For instance, a 18-degree slope contains many small 3-pixel lines combined with a 1-pixel downshift:
This is how nearly every line looks like. Primary element followed by joining and second primary element. Unfortunately, not each slope makes the line look attractive and not annoying.
For example, look at 25 and 20-degree angles:
It can be easily known which line is more appealing. The 25-degree angle produses a line consisting of even 2-pixel primary elements. The 20-degree slope has a basic element consisting of three parts: 3-pixel, 3-pixel and 2-pixel. The slope is more complicated, therefore, when 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 sight.
Now we can see the first conclusion. The most "correct" slopes must make as simple primary elements as possible. Thus, the ideal slopes are 0 and 90 degrees. In them, 1-pixel primary elements are combined without downshift and form smooth lines. Less perfect are slopes which form basic elements of 1, 2, 3 pixel with 1-pixel downshift. Surely, the lines can not be smooth, but the human sight will process the picture and provide to the user what you intended to show to him. Also, the following slopes can be considered acceptable (but at a stretch): slopes with primary elements consisting of different lines shifted by more than 1 pixel.
It is the time to discuss another issue. In the previous paragraph, I intentionally defined angles with basic elements of 1, 2 and 3 pixels as acceptable. Such tiny lines, especially when a large number of them is combined, appear as solid. But what happens if we increase the basic elements to 10 or 20 pixels?
Here is an example:
It can be clearly noticed that the line loses its solidness. It is not a continuous line anymore; it is a combination of different lines, located near one another. Hardly any designer wants its creation to look that way. Thus, we have another rule: if you use minimal angles, which produse long basic elements, it has to be reasoned and used with great caution.
And, finally, the last thing I wanted to tell about lines. I did write that the basic element should be as plain as possible.
For example, a 25-degree angle can be produced 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 picture, it is made of three lines: 3-pixel, 2-pixel and 1-pixel. The same slope but the look is different. The complicated primary element made the line messy.
This examples can be made for about any angle, so in your projects, try to simplify everything.
It can be said without an overstatement that the color is the leading aspect of your work; not suiting or poorly matched colors can kill even the most creative idea. What can we write about the color in miniature graphics?
First, there is a clear rule: if the picture looks bad when reduced to grayscale, it means the colors that were chosen are incorrect. This rule is valid not exclusively for icons but for the whole graphic design.
Second, you will be unable to apply common RGB. Of course, you can use internet 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 areas of "plain" color. The more consistently colored parts without blurring and jumps your composition has, the more neat it appears. Icons are too small and the excess usage of special filters makes the picture look messy.
Fourth, gradients. This is a wonderful instrument which can change the appearance of any composition. Other than esthetics, gradients are a perfect way to get rid of the "broken line" effect (lines with too long primary elements). But be careful when using them because too much gradients can kill the plain color, and be not suitable for the gif palette.
Fifth, shadows and highlights. All rules for applying shades and highlights in icon design are totally identical to the rules of the general graphic design. The only ine I have to note: create everything yourself. Don't apply effects, make all shades and flares in a separate layer and after that edit its transparency. If applying filters, you rarely know what will it look like. It is bad when you can't control the process of creating of a project. It is worse if you can't control it when creating icons.
And, lastly, sixth. Nuancing is the main detail of icon creation, which largely affects the esthetic look of the image. If the blue human eye in the image has the size of 1 pixel, increase the color intensiveness. For example, instead of 0, 131, 159 choose 71, 195, 242. It is indifferent that the human eye never has this color; in the first case it will look like a gray dot, but in the second case it will definitely be a green eye.
completely control the image, do not let the optical illusions to spoil your work. It is OK if something is not consistent from the technical point of view, but the whole image must be flawless.
As an example, I pictured the pack of juice standing in front of me. The picture has plain color, gradients with broken lines, shades and highlights and nuances.
If I talked about something bigger than miniature design, this part wouldn't fit into an entire book, but the resolution of images restricts fonts too.
The size of symbols is the leading aspect as opposed to their fineness. Almost in any case, only if not the letters are the primary part of the project, the text size must be reduced to the largest extent possible.
In general, virtually any graphic company has its exclusive font with little letters. Such a font can be crafted in a few hours. You can browse the web and make your own library of very nice fonts. First of all, I would recommend you to download the DS Pixel and Seventen 7Vedi website as well as the whole set of fonts from the Lakmus Lab website.
If you don't want a new font, small sizes of Arial and Verdana may work. As a last option, you can draw the necessary letters by hand.
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 turns the font into an incomprehensible set of pixels.
Though, there are no rules without exceptions and the 5-point Arial looks perfectly readable.