What is the essence of HTML?newbie question as I am new in web development.

I don't understand what you mean by the "essence" of HTML... can you be more specific?

The "essence" of HTML is knowing the DOM and it's behavior.
I think you want to know a general "best practice" (as edgray said, be more specific) and the main thing is to imagine a browser like a movie image render using your instructions. You can learn a lot of theoretical stuff but the best thing you can do is to practice. So, good luck!

HTML was intended to be a universal mark-up. Universal Access means that the content of a site can be read by a computer using any operating system, any browser (providing it conforms to the agreed standards) and any sort of modem. It can be read on graphical displays of widely-varying sizes, or on machines without a graphical display at all, such as a Braille pad or text-to-speech converter for blind readers. Furthermore, on machines with a graphical display, it can be read with a window size and font size which is convenient to the reader – not necessarily the one which was convenient to the author. The key point is that the computer of the reader does not have to resemble the computer of the author.