For me, one of the keys for something being well written is for the writer to know his limitations before he sits down to write. For instance, Ray Bradbury, when he was alive, could write beautiful, poetic descriptions like nobody's business. He could not, however, do dialogue that remotely resembles actual human speech. Because of this, he very rarely wrote comedic stories or other such pieces where dialogue is key; instead, he wrote novels like Something Wicked This Way Comes and Fahrenheit 451, haunting and powerful works that require the characters to have rather portentous, poetic speech rather than matter-of-fact conversation. Stephen King, on the other hand, recognizes that while his prose is perfectly serviceable, he is no poet; he is quoted as saying "I am the literary equivalent of a Big Mac and fries." What he is good at is telling imaginative, suspenseful stories with characters the reader grows to love, and penning (for the most part) very believable dialogue while doing so. So he plays to his strengths, writing with realist, no-nonsense prose while he draws the reader into his story. For each of these authors, their biggest downfalls come when they try to be something they are not; Bradbury's novel A Graveyard for Lunatics, while it has nice moments here and there, tries too hard to be a realistic noir piece much of the time; many of King's more pretentious attempts at writing (Lisey's Story, among others) quickly become cloying. The good writer must first discover the things he cannot do (this, I have found, involves writing many short stories and submitting them to honest friends to get torn to shreds). Then, he must discover the things he can do, and focus on doing them well.