I've ignored this topic for really long time and I would like to get at least basic instincts on this subject (You know - more than "don't forget to add alt on images").

Assuming that I'm complete noob on this, where should i look first?

Please, do not just post some ISO standards, html spec or whatnot. That will just recoil any interest.

I'm looking for gentle push with guidelines where to look next.

P.s. I did try to find duplicate question/s w/o any luck.