Social skills: Teach them basic manners and table manners; How to network; They will need to learn how to navigate securing internships, jobs and networking with people in their industry.
Environment: Provide an encouraging and nurturing environment for them. Try to shield them from friends and family that show inverted snobbery or those that have that "this is not for the likes of us" mentality.
Confidence: Take acting, or a toastmasters classes so they can speak in public and can engage with others confidently.
Sports and extracurriculars: Encourage learning and trying out different things: Music lessons, martial arts, Tennis, golf, horseback riding, rugby, cricket, skiing... If they can learn the basics, it would be useful for them to engage with their peers and colleagues when they are older.
Culture capital: Visits to museums, art galleries, theatre, woodland walks, restaurants etc..; Watching documentaries and the news; Traveling to different countries and experiencing different cultures;
Academics: Encourage the love of learning, first and foremost. Encourage reading and help them find the subjects they are good at. Then research the careers that tie in with that. Visit universities. Help them find work experience to get a feel for different work environments.
Mentor: Once they have told you what their career interests are, help them find a mentor in that field that can help guide them and give them advice. They can help create a road map of things they need to work on and strive for.
Attitude: Help them develop a hard working nature, build resilience, grit. Give them chores, let them get a part-time job; etc..