When the behaviors most people do in a community aren’t the behaviors most people value, you have a problem.
Your members are creating a large amount of noise and a low amount of signal.
In my experience, this is only going to get worse.
Common examples include posting job links, sharing obscure links, self-promotional posts, beginner-level questions, off-topic questions etc…
You have a few options here:
1) Forbid these behaviors (which probably won’t be popular).
2) Find a place for these behaviors (job boards, promotional zones, beginner areas).
3) Find a time for these behaviors (limit them to certain days).
4) Find the people for these behaviors (get people to subscribe to activities tagged with beginner-level questions, off-topic chatter etc..)
1 and 2 are easiest, 3 and 4 are probably more effective.