Assuming that 20s means post-college:

1) Your ideas are only as good as your relationships.

You are no longer a student surrounded by loving adult mentors who are there to nurture you and help you blossom. Nobody in the real world cares what you think, unless they care about you. So you have to make them care about you!

2) There is no substitute for showing up.

Meetings are 20% about what's discussed at the table, 80% about who is at the table. So be at the table! Yes, it feels like a waste of time and it's much easier to make some excuse at the last minute and stay at home and ask someone to fill you in. But getting "filled in" won't cut it anymore.

3) Responsiveness is the best way to stand out when you're young.

Nobody responds to their email quickly. 50% of people don't respond to their emails at all. Be the person who consistently responds within two hours (or less depending on the industry), and you will make an impression. This goes way farther, early in your career, than anything you can say or produce.

4) Underpromise and overdeliver.

When you are a kid, promises are enough. People get off on your excitement and enthusiasm. If you sign up for 50 different things at the College Activities Fair, and then end up only doing 5, no problem, you still showed your support. If you tell a girl you call her and then don't, no worries, at least you didn't totally blow her off. But that very quickly stops being ok!! Sign up for 2 things. End up doing 5. Don't say you'll call. End up calling. Promise by Friday. Deliver by Wednesday.