Each person has their own, as such, criteria. We observe the people around us, their characters, behavior, gait, some pay attention to their hairstyle / appearance. So, falling in love is probably when you like the outer shell of a person (his laughter, habits). But it also happens that you are simply drawn to a certain person and you cannot explain this: what is it about him, why exactly he occupies all your thoughts. Everyone has their own, personal and, I think, no one will be able to explain it.
Textbooks on social psychology write about this well.
For example, the brilliant old man Eliot Aronson, “Social Psychology. Psychological laws of human behavior in society "
The main prerequisites for rapprochement:
1) The effect of proximity (including the effect of simply being in the field of vision) - as in advertising!
2) Similarity of personality traits
3) We like those who like WE
(somewhat more important for men)
Well, it is worth remembering that falling in love is still a projective feeling: it is not for a person, but for your fantasies, imposed on this person. Love and building relationships begins with ... disappointment!
That is literally: the charm subsides, we find that the person is not what we thought it was. And even very imperfect, that is - real, alive.
If I see a real person and want to build a relationship with him - this is, perhaps, love. And there are patterns too, and see, for example, in the same place))
For example, long-term relationships are more likely to be built when people have a similar upbringing (that is, values), but the temperament is opposite, "complementary" friend friend, etc.