Rules for competent layout or how to use HTML and CSS correctly?

Question

css

Such a problem: knowledge of HTML and CSS does not at all mean their correct application in practice, because the same thing can be done in different ways, using different descriptors and properties.
How to properly use the power of HTML and CSS? Anyone can share? We need such "rules of etiquette" , the rules of competent layout.

Answer 1

For example, here is instanceof.pro/code-guide

Answer 2

Here are those on, well, the question!
How do you understand - knowledge of HTML and CSS does not mean their correct application in practice, but what else should this mean? I now know HTML and CSS inside and out, and this means that I'm not using it correctly?
If you believe the legend, then html is a hypertext markup language, and css is the visual design language for this markup (well, in short). These languages ​​can be used anywhere, in anything, at any time.
Well, for example, Windows 8 applications, mobile applications, html5 games, web applications. These examples can also be implemented in other languages, but this does not mean that you are using HTML and CSS incorrectly.
How to properly use the power of HTML and CSS? Just take and write the markup you need on html, and design this markup through css.