It could happen that some women want to be approached and other women want to be left alone. And then you have the "complicated ones", that are the ones who want to only be approached by someone they like. XD

A (male) friend of mine told me that the secret is to identify which women are receptive to being approached. It had a lot to do with holding their gaze, the way their body was positioned towards him and lots of body language that I didn't caught. But I think he was unto something, because he rarely approached, but the times he did, it usually was welcome.