This is a wonderful question. I had never really thought of how I choose books. I know it’s going to sound cliched but I don't choose books, the books choose me (Harry Potter reference!)
I’m going to try and write the process of choosing a book:-
I should realize and be ready for reading a book. This is very very important because sometimes, we don't feel the need to read.
I make some time for reading. This means, finishing every on going TV series and wasting lesser time on YouTube and time pass.
I make sure that the time is right before the sacred task of choosing a book. You shouldn't be occupied with work or homework or exams while you decide to start reading because when you read a piece of marvel in installments, it’s marvelousness deteriorates.