We discussed priming once before.
The idea is you can prompt people into the right mindset (a participation mindset) when they join.
Most communities are so easy to join that the act of joining carries no significance. If you can sign up in 30 seconds and get a free eBook, it's worth doing.
Far better to prime members to be in a participation mindset when they join. Ask members what they intend to offer the community. Highlight the types of contributions which most help members. Solicit an early contribution/one tip from a newcomer when they join.
Imagine if you replaced the introduction thread with a 'my one tip' thread. Each newcomer would share one tip they have about the topic. It suddenly becomes much more interesting to read and newcomers immediately enter the participation mindset.