/ic/ - Artwork/Critique

I'm struggling with studies, because there's a problem I don't think many videos/text tutorials cover. What happens when you can't see an error and make it worse by "correcting" it?

You can see my study and notice how things spiraled out of control, if i feel the arm is too thicc, how can I know I will make it worse by making it thinner because it turns out i should have slanted it instead? I hope I'm making sense here. I feel like a grid would create a bad habit.