Let's discuss purely technical aspects of icon making
1. Lines, slopes
One of the most important parts of the image is the outline of the object, i.e. solid linear marking, which separates the object from the background. When designing large-scale images, the artist rarely cares about highlighting of objects with additional outlines. This is not needed because of the size: even low contrast objects do not blur into a single whole. Pixel graphics is different. Two variants are available: either object and background colors must be from opposite sides of the color wheel, or the foreground must be divided from the background by contrast outlines and shadows. I would like to dwell on lines in more detail.
If we think again to the large scale images, we can note that in order to highlight contours, we can use any (including the most complicated) angles, Bezier splines and edges. In any case, the line will look ideal thanks to anti-aliasing. When decreasing the image dimensions to the small icon size, situation changes dramatically. When every single pixel is vitally important and can change the whole look of the composition, anti-aliasing is simply unreasonable. It means that you have to think about the possible line angles.
The slope you select for the line, determines the step of this line. This means that every line consists of basic elements, the union of which determines its accuracy and visual appeal.
For instance, a 18-degree angle consists of many tiny 3-pixel lines connected using a 1-pixel downshift:
This is how almost every line looks like. Basic element followed by joining followed by second primary element. Unfortunately, not each slope creates lines that look look neet and not annoying.
For example, here are 25 and 20-degree slopes:
It can be easily known which line is more attractive. The 25-degree angle produses a line consisting of even 2-pixel basic elements. The 20-degree slope has a basic element consisting of three parts: 3-pixel, 3-pixel and 2-pixel. The angle is more complicated, therefore, if not supported by additional visual effects, it creates a feeling of untidiness: the primary elements have contrast which is too obvious to hide from the human eye.
Now we can see the first rule. The most "correct" angles must make as simple basic elements as possible. therefore, the perfect angles are 0 and 90 degrees. In them, 1-pixel primary elements are joined without downshift and form smooth lines. Less perfect are slopes which form basic elements of 1, 2, 3 pixel with 1-pixel downshift. Of course, the lines can not be smooth, but the human brain will process the image and present to the viewer what you intended to show to him. Also, the mentioned slopes can be considered correct (but at a stretch): angles with basic elements consisting of different lines shifted by more than 1 pixel.
It is the time to discuss another issue. In the previous paragraph, I purposely defined slopes with primary elements of 1, 2 and 3 pixels as correct. Such tiny lines, especially when a large amount of them is joined, look like solid. But what happens if we change the primary elements to 10 or 20 pixels?
Here is an example:
It can be obviously seen that the line doesn't have solidness. It is not a continuous line anymore; it is a set of different lines, situated near each other. Rarely any designer wants its composition to look inconsistent. So, we come to another conclusion: if you use small angles, which produse long primary elements, it must be reasoned and employed with maximum attention.
And, finally, the last aspect I have to tell about lines. I already wrote that the primary element should be as simple as it can.
For example, a 25-degree slope can be produced in the two (of course more of them exists) following ways:
In the first picture the primary element is a 2-pixel line. In the other picture, it is made of three lines: 3-pixel, 2-pixel and 1-pixel. The same slope but the look is different. The complicated basic element made the line untidy.
Such examples can be produced for almost any angle, so in your projects, try to simplify as much as possible.
It can be stated without an overstatement 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 miniature 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 only for icons but for the entire graphic design.
Second, you will be unable to apply safe RGB. Sure, you can select GIF colors only, but this limits you greatly. Gradients, shadows, blending and many other effects will not be accessible to you.
Third, try to enlarge the areas of "flat" color. The more consistently colored areas without diffusion and jumps your project has, the more neat it looks. Pictograms are too tiny and the over usage of complex filters makes the image look messy.
Fourth, gradients. This is a great instrument which can change the appearance of any picture. Other than esthetics, gradients are an ideal way to abolish the "broken line" effect (lines with too long basic elements). But be careful when applying them since too many gradients can ruin the flat color, and be unable to fit into the gif palette.
Fifth, shadows and flares. All rules for using shadows and flares in icon design are completely identical to the aspects of the general graphic design. The only thing I would like to mention: draw everything by hand. Don't apply filters, make all shades and flares in a separate layer and after that edit the opacity. When applying filters, you almost never can predict what the result will be. It is unfavorable when you can't control the making of a project. It is awful if you can't control it when creating miniatures.
And, lastly, sixth. Nuancing is the main detail of icon design, which greatly affects the visual appearance of the project. If the blue human eye in the image has the size of 1 pixel, increase the color saturation. For instance, instead of 0, 131, 159 choose 71, 195, 242. It is indifferent that the human eye never has such color; in the first example it will look like a gray dot, but in the second example it will really be a green eye.
Thoroughly control the picture, do not let the optical tricks to ruin your work. It is acceptable if something is not consistent technically, but the whole picture must be flawless.
As an example, I pictured the pack of juice located before me. The image has flat color, gradients with broken lines, shades and flares and nuances.
If I talked about something other than icon design, this part wouldn't fit into a whole book, but the size of compositions ;limits fonts too.
The resolution of letters is the leading issue as opposed to their look. Nearly in any case, unless the letters are the main part of the composition, the font size must be decreased to the greatest extent possible.
In principle, almost any graphic studio has its own font with small letters. Such a font can be made in a couple of hours. You can search the internet and collect your own collection of very interesting fonts. Primarily, I would recommend you to get the DS Pixel and Seventen 7Vedi website as well as the complete set of fonts from the Lakmus Lab website.
If you don't need a new font, small sizes of Arial and Verdana will do. As a last resort, you can draw the needed characters 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 text into an unrecognizable mixture of pixels.
However, there are no rules without exceptions and the 5-point Arial appears perfectly understandable.