I mostly consider 4 things when rating a book: plot/pace, quality of writing, characters and relationships/romance. I also sometimes include a spoiler section if there are any mind blowing plot twists/conclusions that I want to talk about with those who have read the book.
5 Stars: I LOVED the book and I will recommend it to anyone.
4 Stars: I really enjoyed the book but there was something lacking that would’ve pushed it over to a 5 star read.
3 Stars: I found the book alright but it wasn’t amazing or terrible.
2 Stars: The book was not my cup of tea but it had some qualities that I liked.
1 Star: I really don’t like the book. (I basically never give 1 stars to books though.)