I have never learnt the basics of art, like composition and colour theory. I am studying them now though, I bought a bunch of books. It's a must if I am going to master this art thing! I've never used grids either until last week, it's very useful, I tend to elongate my faces when drawing portraits, the grid system helps stop this a lot. I'm still learning so much, even today, three years after starting to draw and paint again.