According to Harold G. McCurdy, a professor at the University of North Carolina, the first step was to not send your kids to public school.
Not that he had anything against public schools, having sent his own kids to one. And he questioned whether raising kids to be geniuses was a desireable goal, since he believed that geniuses often led isolated, unhappy lives.
Nevertheless, based on his study of the childhoods of 29 geniuses, conducted back in 1960, he determined that “three striking factors seemed to be typical of the childhood pattern of genius”:
“Public school education,” he declared, “works against these three things.”
Apparently McCurdy’s study has been embraced by some proponents of home schooling. Although I don’t get the sense that it was his intention to promote that.
You can read McCurdy’s full study here: The Childhood Pattern of Genius