People spend more time interacting with their friends than strangers. This isn’t new information. If your community members are friends (real friends, not connections), they’re going to participate in the community a lot. In the best communities, members are close friends.
Friendships develop in a standard pattern. People meet, find an area of similarity (usually the reason for their meeting) and begin a series of conversations.
These conversations begin by discussing safe (common-interest) topics. Gradually, participants will reveal more about themselves. This is tit-for-tat. I reveal my opinion on politics, and so do you. This reciprocity builds trust. Gradually we’ll reveal details about our past, our hopes and fears, and many other intimate details.
Self-disclosure is why participation works. By revealing more about ourselves through our personal information, our emotions, our thoughts/feelings, our history etc and learning more about others we feel a strong sense of connection with them. The more we reveal the more we emotionally invest in the community.
Mirroring the development of friendships. You need to move members gradually from discussing safe topics to revealing more about themselves.
You begin by providing newcomers with simple profile answers to fill out. Keep these safe, fun and interesting. Allow comments on these and there should be a great reason for newcomers to make the second visit.
Then ensure there are always opportunities for people to reveal more of their opinions. There are plenty of questions you can ask to stimulate discussions that encourage this self-disclosure. Mix these up between opinions, experiences and emotions (hopes and fears).
Also draw attention to controversial issues that people have strong opinions about. Don’t shy away from conflicting opinions. Disagreements are good for encouraging self-disclosure.
You will need to stimulate this in the beginning, all founders do, but over time members will begin initiating most of these conversations themselves.
Over time this steady and ongoing process will build strong friendships between members of your community, which increases the community's lifespan, increases value and leads to high levels of participation.