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I've recently come back to this site because, frankly, I really need help.
I know theory, but have a hard time putting it into practice. I don't quite know how to paint and render images properly since i don't understand shading by color (or,well, shading of features/shapes in general)
Apart from that, I'm utterly shit at placement and proper arrangement.
Critique on this WIP VERY welcomed, as well as any links to tutorials you found helpful!
Get an apple and paint it. Then find something else and paint it. Take your time with these and don't stop till it looks real. You'll have the ability to paint sooner than you think. It actually kind of sneaks up on you when you do this.
That's the single most useful thing you can do.
I agree with David, you just need practice. But if I were you I'd ignore colour until you get a better sense of value and how to render shapes in b&w. Take a step back and work on fundamentals. There is no rush to try and create epic art. You need to learn how to build a house before you can paint it. Good luck.