So basically you have to post a lot of messages to grow in rank.
Is there a minimum of characaters and does it needs to be on topic?
Otherwise you will just spam through levels right?
You have to understand the formula, just random posting things won't work.
The formula:
time =number of two-week periods in which you've posted since your registration
activity = min(time * 14, posts)
That means that every two weeks since you posted (and I believe you gotta keep posting in these 2 weeks) the factor 'time' will go up 1. It is true that the more you post the higher your activity will be, but the formula will take the amount of posts, or the time * 14. So to become a jr member you have to be at least 6 weeks member and have at least 30 posts.
Hope you understand