This is where beta readers come in. Beta readers give the feedback and suggestions which can take a mediocre second (or third or fourth) draft (I would never give anyone a first draft to read) and help the author turn it into an amazing published book.
In order to do so, beta readers need to be able to give constructive criticism because neither saying "Oh, it's good. I loved it" or tearing the whole thing to shreds is helpful to the author. A good beta reader will note both good and bad points of the story/setting/characters, be able to point out anything they found confusing, and generally pass along suggestions for improvement.