Ask HN: What people skills do you wish you learned earlier in your career?

For the past several years I've been putting in a lot of time into learning and sharing people skills (without the bullshit).

I'm interested in skills from dealing with your own emotions, through communication with close co-workers to high-stakes negotiating.

I'm curious: what are some people skills that you wish you had learned earlier in your career or that you wish your co-workers had easier access to?

Also: what are your favorite books and/or other resources that helped you?