The above are all really good points that I definitely agree with. I didn't however see anyone mention one very vital piece to me; Communication.

An FC is only as strong as some of its leadership but to me a good FC, even with only average leadership, could still net great benefits as long as there is significant communication amongst the group - Not just to talk shop and strategies but to just talk with, bond, garner relationships and be social. For some people this game can be a significant outlet socially for them, and for others it might just be tertiary, but either way forming these friendships with likeminded people who you can joke with, talk with, etc., will ascertain a higher retention for the free company, and I think ergo, a higher rate of success.