What are the best predictors of "social success" (friends, relationships, job, etc.)?

One might say that the among SAT scores, high school GPA, recommendations and essay, one’s SAT score is the best predictor of academic success in college. Well what if we pivoted this question to the social realm. I’m interested in hearing what people would consider predictors of “social success”—those traits, experiences, behaviors, activities, etc. which makes certain people good with people and relationships in general in social, romantic and work contexts. It seems to me that certain people are simply very good with people, and thus in life in general, whereas certain other people are not—but it is not always evident exactly why this is, as well as how those who are not as successful socially can improve their social skills. An interesting corollary question might be, what are the predictors of social failure?