I was in a wonderful poly relationship for five plus years.
During the times it was really working well we were really practicing the "communicate, communicate, communicate" mantra. When we started taking communication for granted was when we started to run into problems. I would generally advise people to find as deep a level of communication as they can uncover.
1) Find partners that are worthy of your trust.
2) Trust them. Allow yourself to be vulnerable. Be useful when they are vulnerable.
3) Communicate. Learn more about the story of them and teach them more about the story of you. Know them and what it is they need to help them grow in the direction they're growing.
4) Love like your life depends on it (because it does) and do what love requires of you.