I am a newbie. How can i rank up quickly to jr or higher membership. I continuously posting everyday. But my activity is not being increased. Then what can i do? Actually i don't know the activity counting system.
Irrespective of your posting, your account will get promotion as per the rules defined by the forum management. Refer the link posted by mjglqw above.
However, it is not recommended to post just for the sake of ranking up, Bitcointalk is a huge community of resources to learn about Bitcoin and cryptocurrencies so one should seek knowledge instead of posting especially in his initial days.
Bonus tip: If anyone finds that you are posting spam then they may give you a red trust feedback for it and it will make your account less trustworthy so think thrice before posting.