See at a glance:
0 Posts: Brand New
1 Activity: Newbie
30 Activity: Jr. Member
60 Activity: Member
120 Activity: Full Member
240 Activity: Sr. Member
480 Activity: Hero Member
775-1030 Activity (random): Legendary
Need to be active like what others told you but you must remember that you should post or make flood post in one day because you might be ban like other told me due to spam post. Also it takes 1 yr to be a sr. Member to a legendary. So my suggestion is you should make 5 or 6 and depends how your campaign make the rules of posting. Like 20 in one week 3or 4 and 5 post in day .
Why is it important to get Sr rank?
You got your answer here but I would like to suggest....
As for a sr. Member sometimes you get paid higher than a full member but still depends on the campaign if it successful or depends on the participants but sure you get paid high but not hight than the legendary rank.
You really need to take note of this one too so good luck to you.
How many activities does it take to be a sr. member??
240 < activity
By the way mvillar you should not post simple numbers to a reply its helpful but you should atleast make it constructive dont post things like that you should post more than that someone might report you or the moderator can see this and delete it due to low quality post you made.