The most important would be a desire to learn and a love of reading. I was taught early on if you can read - you can do anything.
Critical thinking skills would be next - not the "no child left behind" system of teaching to tests we have now. Kids memorize a bunch of stuff with no clue as to how anything actually works. Our system encourages complacent robots, not innovators. Most young people can regurgitate information and push the right buttons, but have no passion to know "why" things happen or "how" they came to work that way etc.
I think next would be a respect for but healthy skepticism of tradition that is merely for the sake of tradition - for example voting the same way your parents do because that's just what you do. Religion is another one - people tend to just do things that are customs without questioning them or feeling free to be critical of things that are outgrown. I think allowing for authenticity is a great gift to a child.
Teach them empathy for others, combined with a strong sense of self. I believe the best leaders are those who value themselves enough to want to be their best, but not at the expense of those around them. Truly successful people want to encourage others to do their best also - not just stomp all over others to get ahead.
Allow your kids to fail - early and as often as necessary. We have such a society of pansies anymore - you can't really compete, every special little snowflake is a winner. While it's great to push self-esteem, when you eliminate all real competition kids grow up not understanding that failure is a part of life and then when the real world comes up - they have no idea how to handle themselves and crumble under the pressure and accept failure or mediocrity. All these helicopter parents... so annoying. Their kids grow up feeling entitled to be the "best" at everything without really having to push and work hard. They have no problem solving skills because they are too sheltered.
Finally, participate in your kid's life. So many people shove their kids in front of TV, video games, phones etc. and willfully participate in turning their kids into zombies - I know that sounds harsh, but there's a reason they call the TV an "idiot box". Social skills are so lacking in a lot of younger people. Talk, engage, participate face to face, take an interest.