how my rank goes up
Your activity will increase every biweekly period, maximum increasing is 14 points if you make 14 posts in that period.
No problem if you can't make 14 posts in that period, you can "save" potential activity by just make one post, and post later for rest of activity increasing.
If you want to know when actually activity increasing in biweekly period, just visit this thread
https://bitcointalk.org/index.php?topic=582736.0;topicseenit is very helpful thread