Let's consider purely technical aspects of icon creation
1. Lines, angles
One of the vital elements of the image is the outline of the object, i.e. solid border, which limits the object from the background. When designing normal-sized graphics, the artist occasionally thinks about highlighting of objects with complementary outlines. This is not needed because of the size: even low contrast objects do not blend into a one. Icon graphics is different. Two solutions are possible: either object and background colors have to be from different sides of the color chart, or the foreground should be separated from the background by visible outlines and shadows. I will discuss lines in more detail.
If we return again to the big-size graphics, we can note that in order to highlight contours, we can use all (including the most complicated) angles, Bezier splines and edges. In any case, the line will appear ideal thanks to anti-aliasing. When shrinking the image scale to the size of an icon, situation changes dramatically. When every single pixel is equally important and can ruin the overall appearance of the icon, anti-aliasing is just not applicable. It comes that you have to consider the possible line angles.
The slope you choose for the line, determines the step for this line. This means that every line consists of basic elements, the combination of which determines its accuracy and esthetics.
For example, a 18-degree angle contains many small 3-pixel lines connected using a 1-pixel downshift:
This is how almost each line looks like. Basic element with joining followed by second basic element. However, not every angle makes the line look attractive and not messy.
For example, here are 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 basic elements. The 20-degree angle has a basic element containing of three parts: 3-pixel, 3-pixel and 2-pixel. The slope is more complex, thus, if not combined by additional 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 come to the first conclusion. The most "correct" slopes must make as simple primary elements as they can. therefore, the ideal angles are 0 and 90 degrees. In those, 1-pixel basic elements are joined without downshift and form even lines. Less perfect are angles which form primary 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 image and present to the viewer what you meant to show to him. Also, the mentioned angles can be considered correct (but at a stretch): slopes with primary elements made of different lines shifted by more than 1 pixel.
Now we can touch another problem. In the previous paragraph, I purposely defined angles with primary elements of 1, 2 and 3 pixels as acceptable. Such small lines, especially when a great amount of them is combined, look like solid. But what happens if we increase the basic elements to 10 or 20 pixels?
Here is an example:
It can be obviously seen that the line doesn't have integrity. It is not a continuous line anymore; it is a combination of several lines, located near one another. Hardly any artist wants its composition to look that way. So, we have another rule: if you use small angles, which produse long basic elements, it must be reasoned and used with great attention.
And, finally, the third aspect I have to mention about lines. I did write that the basic element should be as plain as it can.
For example, a 25-degree angle 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 picture, it consists of three lines: 3-pixel, 2-pixel and 1-pixel. The same angle but the image is different. The complex basic element made the line messy.
Such examples can be made for almost any angle, so in your projects, make sure to simplify as much as possible.
It can be stated without an overstatement that the color is the main element of your work; not suiting or poorly matched colors can ruin even the most creative idea. What can we write about the color in icon graphics?
First, there is a clear rule: if the picture looks poor when reduced to monochrome, it means the colors that were selected are wrong. This rule is true not exclusively for icons but for the whole graphic design.
Second, you will be unable to use safe RGB. Of course, you may use internet colors only, but this limits you greatly. Gradients, shadows, dithering and many other effects will not be accessible to you.
Third, try to increase the areas of "plain" color. The more consistently colored areas without blurring and jumps your composition has, the more clear it looks. Icons are too small and the over usage of complex filters makes the picture look messy.
Fourth, gradients. This is a great instrument which can change the appearance of any picture. Besides esthetics, gradients are a perfect solution to abolish the "broken line" effect (lines with too long primary elements). But be careful when using them because too many gradients can kill the flat color, and be unable to fit into the gif palette.
Fifth, shadows and highlights. All rules for using shadows and highlights in icon making are totally identical to the aspects of the overall graphic design. The only thing I would like to mention: create everything yourself. Don't use effects, make all shades and highlights in a separate layer and then edit the opacity. If applying filters, you almost never can predict what the result will be. It is unfavorable when you don't control the making of a composition. It is worse if you can't control it when drawing miniatures.
And, finally, sixth. Nuancing is the main detail of icon creation, which largely results the visual look of the image. When the blue human eye in the image has the size of 1 pixel, increase the color intensiveness. For instance, instead of 0, 131, 159 choose 71, 195, 242. It is indifferent that the human eye can't have such color; in the first case it will look like a gray dot, and in the second example it will definitely be a green eye.
Thoroughly control the picture, do not let the optical tricks to ruin your work. It is OK if something is not perfect technically, but the whole picture must be flawless.
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 tints.
If I wrote about something other than pictogram creation, this chapter wouldn't fit into a whole book, but the resolution of pictures restricts fonts too.
The resolution of letters is the main aspect as opposed to their fineness. Nearly in all cases, unless the letters are the primary part of the composition, the text size must be decreased to the greatest extent possible.
In principle, almost any design studio has its unique font with small letters. This font can be made in a few hours. You can search 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 set of fonts from the Lakmus Lab website.
If you don't want a new font, small typesizes of Arial and Verdana may do. As a last option, you can draw the necessary characters by hand.
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 incomprehensible set of pixels.
Though, there are no rules without exceptions and the 5-point Arial appears perfectly readable.