I'm limited by my ability to only be able to bring stuff up to talk about when I see something that I think can be improved. As far as what I look for in high quality art and notice when it's absent,
this article covers the bases. The fundamentals of art are nebulous concepts that become more concrete as an artist develops their own skill.
edricluffie works in the same space as I do, painting realism/semi-realism, so my gaze is attuned to such styles and I can pick stuff out easier. When it comes to work as high quality as edricluffie's usually I can only pick out one or two things that I can see need improvement because they're at a higher skill level than I.
However, for artists below a certain skill threshold, it's easier to instruct them how to develop their fundamental art skills further rather than pick out every little thing that needs improvement. Which, for beginners, in there work there's vast rooms for improvement.
If you want advice, I can dispense it more effectively when I have an artwork I can critique. I know KF probably isn't the place people even want unsolicited critique, but I like helping people.