1. They make their kids do chores.A few things in this list are more "nature" than "nurture." Education levels, healthy relationships, and socioeconomic status tend to be more genetics than they are directed effort, which is to say, things over which parents have little control. Relevant to children's success nevertheless, perhaps even more so.
2. They teach their kids social skills.
3. They have high expectations.
4. They have healthy relationships with each other.
5. They've attained higher educational levels.
6. They teach their kids math early on.
7. They develop a relationship with their kids.
8. They're less stressed.
9. They value effort over avoiding failure.
10. The mums work. (translation: moms)
11. They have a higher socioeconomic status.
12. They are "authoritative" rather than "authoritarian" or "permissive."
13. They teach "grit."
Many families of my acquaintence have disappointing adult children even though the adults are successful people who remain married and have decent social skills. A psych teacher I had years ago called this "reversion toward the mean," by which he meant bright, successful people are out-of-the-ordinary and their children will often be less exceptional, more ordinary.
Hat tip to Lucianne.com for the link.