Here's a simple structure I use to evaluate the non-fiction (books, articles, essays, etc) I read:
Is it true?
Does this explain the world in some way? Does the information appear to correspond to how things work in the world, given prior knowledge and experience? Does the material cite sources? Does the material abuse cognitive biases to appear more appealing or persuasive?
Is it useful?
Can this be applied to produce better results in important areas, or is it an intellectual form of entertainment? Is there a clear next action from reading this material? Does the material suggest things to do or try? Are you taking notes to apply the material when you finish reading?
Is it clear?
Does the author / essayist present the information in a way that makes the information straightforward to understand and apply? If the subject matter is technical or challenging, do they attempt to make it more approachable? Do they anticipate and answer objections or common barriers to understanding?
The best material has all three qualities. If it's not true, not useful, or not clear, it's probably best to find another resource unless your purpose is entertainment.
This framework also happens to be a good starting point for writing non-fiction. If what you're working on isn't true, useful, and clear, you still have work to do.
Special thanks to Ben Casnocha - we discussed this over tea a few months ago. The importance of clarity is Ben's contribution, and his comments changed my thinking on this topic. I'm more willing than most to wade through the obscure, so I was originally willing to settle for true and useful.