Let's discuss strictly technical aspects of icon design
1. Lines, slopes
One of the most important parts of the image is the framework of the object, i.e. rough border, which limits the object from the background. When creating large-scale images, the designer occasionally cares about defining objects with complementary outlines. This is not needed because of the size: even low contrast objects do not blend into a single whole. Pixel graphics is other story. Two solutions are available: either object and background colors have to be from different sides of the color wheel, or the foreground must be divided from the background by contrast lines and shadows. I would like to dwell on lines deeper.
If we think again to the big-size images, we can note that in order to define contours, we can use any (even the most complex) angles, Bezier splines and borders. Anyway, the line will look ideal due to anti-aliasing. When shrinking the image scale to the size of an icon, situation changes dramatically. When every single pixel is vitally important and can ruin the overall appearance of the composition, anti-aliasing is just not applicable. It comes that you have to consider the possible line angles.
The angle you choose for the line, specifies the step of this line. Because each line consists of primary elements, the union of which determines its neatness and visual appeal.
For instance, a 18-degree slope contains many tiny 3-pixel lines combined with a 1-pixel downshift:
This is how nearly every line looks like. Primary element with joining followed by another primary element. However, not each angle makes the line look neet and not annoying.
For example, look at 25 and 20-degree slopes:
It can be easily seen which line is more appealing. The 25-degree slope makes a line consisting of even 2-pixel basic elements. The 20-degree slope has a basic element containing of three lines: 3-pixel, 3-pixel and 2-pixel. The angle is more complicated, therefore, when not supported by other 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 come to the first rule. The most "appropriate" angles must make as simple primary elements as possible. therefore, the ideal slopes are 0 and 90 degrees. In them, 1-pixel primary elements are joined without downshift and produce smooth lines. Less perfect are angles which form basic elements of 1, 2, 3 pixel with 1-pixel downshift. Of course, the lines will not be even, but the human sight will process the picture and provide to the viewer what you intended to show to him. Also, the mentioned angles can be considered acceptable (but at a stretch): angles with basic elements made of unequal lines shifted by more than 1 pixel.
It is the time to discuss another problem. In the last paragraph, I purposely defined angles with primary elements of 1, 2 and 3 pixels as acceptable. Such tiny lines, especially when a large amount of them is combined, look like a single whole. But what do we see if we increase the primary elements to 10 or 20 pixels?
Here is an example:
It can be obviously noticed that the line loses its integrity. It is not a single line anymore; it is a combination of several lines, situated near one another. Rarely any artist wants its creation to look inconsistent. So, we come to another rule: if you use small slopes, which make long primary elements, it has to be justified and used with maximum caution.
And, finally, the last aspect I wanted to tell about lines. I did write that the basic element should be as plain as it can.
For example, a 25-degree slope can be produced in the two (sure more of them are possible) following ways:
In the first case the primary element is a 2-pixel line. In the other case, it consists of three elements: 3-pixel, 2-pixel and 1-pixel. The same slope but the image is different. The complicated basic element produced the line untidy.
This examples can be produced for almost any angle, so in your projects, try to simplify as much as possible.
It can be said without an exaggeration that the color is the leading aspect of your work; not suiting or poorly balanced colors can ruin even the most creative idea. What can we say about the color in icon graphics?
First, there is a certain rule: if the image looks bad when reduced to grayscale, it means the colors that were used are wrong. This rule is true not only for icons but for the entire graphic design.
Second, you will be unable to use common RGB. Of course, you can select internet colors only, but this limits you greatly. Gradients, shadows, dithering and many other effects will not be accessible to you.
Third, try to enlarge the portion of "plain" color. The more evenly colored parts without blurring and jumps your composition has, the more neat it appears. Pictograms are too small and the over usage of complex filters makes the image look messy.
Fourth, gradients. This is a wonderful tool which can change the look of any composition. Besides visuals, gradients are a perfect way to abolish the "broken line" effect (lines with too long primary elements). But be careful when using them because too much gradients can kill the flat color, and be unable to fit into the gif palette.
Fifth, shadows and highlights. All aspects of applying shadows and flares in icon creation are completely identical to the rules of the general graphic design. The only ine I have to mention: create everything by hand. Don't apply effects, make all shades and flares in a different layer and after that edit the opacity. If applying effects, you rarely can predict what the result will be. It is unfavorable 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, finally, sixth. Tinting is the main aspect of icon creation, which largely results the esthetic appearance of the image. When the blue human eye in the picture has the size of 1 pixel, increase the color saturation. For instance, instead of 0, 131, 159 make 71, 195, 242. It is indifferent that the human eye never has this color; in the first case it will appear like a gray dot, but in the second example it will really be a blue eye.
Thoroughly control the picture, do not let the visual illusions to spoil your design. It is acceptable if something is not consistent from the technical point of view, but the whole image must be flawless.
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 highlights and nuances.
If I wrote about something bigger than icon creation, this chapter wouldn't fit into a whole book, but the resolution of compositions ;limits fonts too.
The size of symbols becomes the leading issue as opposed to their look. Nearly in any case, unless the letters are the main part of the image, the font size has to be reduced to the largest extent possible.
In principle, virtually any graphic company has its unique font with little letters. This font can be made 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 webpage as well as the complete series of fonts from the Lakmus Lab website.
If you don't want a new font, tiny sizes of Arial and Verdana will work. As a last resort, you can draw the necessary characters yourself.
There are not many rules there. First, letters cannot be less than 5 pixels high or less than 3 pixels wide.
Second, letters should not use anti-aliasing. It transforms the font into an incomprehensible mixture of pixels.
Though, there are no rules without exceptions and the 5-point Arial looks perfectly readable.