Strange, usually no one talks about it, but there is the most important principle. Usefulness. You can draw a large set by following all these principles. Put beautiful creative images. But if no one wants what you've drawn, it's all pointless. An example is the video cassette or CD icon. You can go even further and take a punch card as an example. I've seen a lot of icons with a reel of film for the photocamera, but no one needs them. This, by the way, applies not only to icons, but also to design in General.