Basically, 由 being an active member of a club and contributing things which others like: 1. Getting the links, articles, 图片 and 视频 you've added fanned 2. Answering lots of questions, 民意调查 etc. 3. It's easier to get 奖章 in 更多 active 俱乐部 than dormant ones.
I don't think there's a set number of 粉丝 或者 contributions. The system's pretty random. Sometimes it doesn't really make sense.
