Anatomy, lighting, light vrs dark, fundamentals, perspective etc etc etc.
There are so many topics to practice to be a good artist.
But you don't HAVE to work hard daily and stress yourself out. What makes you a good artist is passion. if you have passion you work and better yourself. If you don't, you dont. With passion its not stressful its not hard work its fun and enjoyable and hours on hours and hours go through the roof. Sometimes you miss sleep, sometimes you forget to eat. You get lost in a new world away from the rest of the world for a while and just kinda warp out alittle.
With passion you will learn all the fundamentals. Because you want to. You want to be better, you want to be a great artist. See, i thought i had passion with art. So i worked and worked and worked but it was stressful. Now i found something i AM passionate for. Its science.
Point is, programming and learning things is easy. Because i have the passionate drive to do it. I sit down for 10 - 12 hours a day and just program and work on math formulas.
I never did that with art.
So don't let people scare you telling you you have to do this you have to do that. It's a lie. If your passionate, no matter what you will be good at what you do. Because you put the time required into it, not only that your all smiles about everything and its just an enjoyable expierence.
Not everyone lives life having expierenced true passion. So don't let yourself get consumed into thinking you HAVE to do this. You don't.