Tl;dr; The very first and basic thing to do is to encourage users to become volunteers.
All users in any community have some unique talents. Your task is to provide them with opportunities so that they can show off their talents to the best of their ability. Users may be shy, afraid of criticism, or don’t know where to start. You need to support the users morally, instill faith in them that they will succeed and should try.
The ability to positively impact many people through initiatives in your community is an effective motivator that may encourage users to become more active.
This is a fragment of a draft of the book “Lessons Learned While Working On Stack Overflow”. Read the full book on kindle or the paperback version.