A very underrated topic, that I literally haven't seen being mentioned in any beginners course. So let me be the one to mention it.
Styleguides are documents, that describe how to write code. Global Web Standards are defined in documents, that are not quite styleguides, but an effective code rule list, that aims to increase the quality of websites in the world. How? It contains rules, that enforces, for example HTML Image elements, to also have a text attribute, that would allow people with sight impairments to have the image be described by their specialized software.
Of course you can write code however you want, but doing so without any foresight will really confuse not only your future self, but other developers too. That's why styleguides were invented. It's a document that outlines coding conventions that the developers will use, for that project. Usually they are defined for projects individually, based on the recommendations of developers that will work on it.
Generally, it doesn't hurt to look into some that are available online:
Because many conventions are shared across projects, teams and even languages. The point here, is to be aware that such systems exist and when in doubt on how to write something (and not be afraid of showing it off in an interview), use recognized company styleguides as a basis. If it works for a company with a multiple figure revenue well enough that they're not afraid to put it out there, probably will work for you too.
Depending on how you memorize stuff best, it might help to create a cheatsheet. Maybe even a beautiful one! Like @_georgemoller did in his recent tweet about GitHub CSS Best Practices:
As mentioned, accesibility is only one of the many aspects governed by the global web standards. But who governs the web standards? The World Wide Web Consortium is an international community, where many different people develop a standardized document, outlining the best practices for creating websites and web-based solutions. It's being led by the inventor of the Web (duh, obviously) Tim Berners-Lee and CEO Jeffrey Jaffe.
"So - what, you expect me to follow every change they make to the standards and forever be dependant on them?"
No. Kind of. Maybe.
You don't have to read any documentation that's on their page. You just let your site get scanned by their "Nu HTML Checker". It will show you all warnings and errors, where you've broken rules of HTML standards.
"Why should I care? I am a rebellious soul and I want havoc."
Sure. Though beware of these two things:
Of course, there are many other factors too, but these 2 are just practical examples from the top of my head.