How do critics, reviewers, and publishers yze books?

i read a lot of books, but im terrible at reviewing them as a critic would. what are professional critics (like the ones in newspapers and magazines) looking for when reading a book? whenever i read a book i seem to enjoy it no matter what. but then sometimes when i read a critic's review they will criticize on something i never picked-up. so again, what are the looking for? and how do they pick-up on it?