I agree with you asking about books, it often tells me a great deal, particularly when the other person indicates that they don’t read books. I also agree with @Sunny2 about just asking the person, but I am a big observer. I look at people’s clothing (particularly shoes) to tell me how much they care about fashion or comfort. I look at the wear pattern on the shoes to give me a sense of how much money someone spends on shoes (a practical item in my book, not a fashion statement).
I also look at teeth and fingernails to see how a person cares for him or herself. I can usually tell the guitar players and can gauge the hard-workers by the callouses when I shake hands. I look at hair to see if it has been recently cut, did the person style it, add product, etc. I also take in the jewelry choices: earrings, wedding rings, other rings, bracelets, etc. to give me a sense of the other person’s interests.
Perhaps I should also tell you that I am OCD and observations and assessments are a big part of how I look at the world. When I was in about 8th grade, our English teacher was sitting at his desk when a man entered the room and assaulted him. It was an unexpected lesson in observation (for use in creative writing). We each had to describe the person. I nailed it, capturing the clothing, gender, hair, etc. Many other students missed a number of critical elements of identification of the assaulting party—gave me a very keen understanding of the problems with “eye-witnesses.”