The answer is quite simple but it's hard to achieved it. Getting merits from other users is the only way to increased your rank. You will need a lot of patience and hardwork to be able to do so. You can make your own thread or post in a thread with a good quality post that serves useful information for the others.

To achieve Jr. Member rank is easy, you'll only need 1 merit and 30 activity and for you to become a member, you'll need 10 merits and 60 activity. To get merits is very challenging. I also find it hard but i always do my best. You also need to keep this in mind NEVER BEG FOR MERITS to other users as it will get you Red trust and it is bad for your image and could make it harder for you to get accepted when you apply campaigns.