30 activity is what you need. I was tempted not to say that because it is already answered by many.  One thing I have to share here is be active. I often heard and read that you will be Jr if you have 30 activity in one month, but my experience here is very surprising because a was ranked up into Jr member in just 3 weeks. What I did is giving a constructive post and always find time to be online and make a read. If we take bitcoin seriously we will not get disappointment.