313RN is right on.
Set an example. Always offer help. If an IV is beeping, go check it, don't just call the nurse and let her know.
Other things we do:
We have nights out every once in a while. I simply send out an email to everyone on the floor saying we're going to meet at X bar at 7pm for 2 hours. Usually about 5-8 people come, and they are usually not people I typically hang out with. I love getting to know my coworkers outside the bar.
A lot of times we do something very informally. Day shifters go out for a late dinner or drinks after work, and it's usually scheduled on that day. They just decide to go out, invite everyone who worked that day, and about half of them end up going.
On nights, we try to go out for breakfast, particularly on a weekend. Sometimes we just meet in the cafeteria, sometimes we go somewhere else. Once again, I make a point of inviting everyone. Even if you don't go, just being invited is nice.
None of this is official, or comes from management...it's just something that someone, anyone organizes and invites other to. When I organize an evening out or a breakfast, I always do it with one other person--that way I know at least one person will be there with me.
Some people don't like going out to a bar--I tell them that's fine, organize us to do something else. Bowling, dinner, a movie, whatever.
My point is, take initiative. Be the team player. Be the nice, smiling, positive nurse. Organize a night out with a coworker and invite everyone.