I see a number of things out there that address the issue of writing quality, including some posts here. But I wanted to ask the question of writing quality with a specific eye to my experiences. As a college graduate, I've had to write papers for several classes related to a number of disciplines. This has presented a number of opportunities for my writing to be critiqued, and has presented some points for improvement.
The problem comes in this: Those critiques have been wildly inconsistent. I've had papers that have been flunked over "writing issues", and other papers that have gotten high grades. I even have one instance where a professor suggested that papers be reviewed by the school's writing lab. The people there praised the paper and even used the phrase "you write wonderfully", but the professor docked 40% of the possible grade for this paper for "writing issues". Thankfully, this professor was fair about his suggestion blowing up in his face (I surmised that my paper wasn't unique in this way) and offered a second chance at the grade with his "writing issues" pointed out. Needless to say, this is frustrating when determining what I actually do need to improve. My guess is that a true critique of my writing lies somewhere in the middle.
So with that in mind, how do you determine what you genuinely need to improve upon when it comes to your writing skills? Proofreading and review by others is an obvious answer. But how do you tell when a critique is "too easy", or more important to the question if something is just a personal pet peeve from a grammar, word-choice (or otherwise) standpoint?