Science and life experience have taught us likeable people have many of the same qualities. I say life experience because in life we learn as we go along. The person I was my teenage years and in my 20's is much different than who I am now. I always try to keep this in mind when I talk to the younger people I work with and my 4 kids.
1. Being arrogant, rude or superficial won't get you very far.
2. Be Transparent. Tell the whole story and admit your mistakes.
3. Be sincere.
4. Be understanding and a patient listener
5. Encourage others
6. Stay positive
7. Be curious
One thing I might want to add is having a good sense of humor. I've survived several tragic situations and events through the years. One thing that helps is still being able to see life's funny moments.