Read the posts that got merit and try to figure out quality or information in that post.
Post original and creative content.
Keep on posting.
It would be really good to apply some of what you wrote to yourself, because apart from 500 airdropped merits you didn't earn any. "Keep on posting" just to fill the quota of posts needed for a signature campaign is very bad advice. It's better to post nothing than to post zero value content, or to beat dead horse in mega-threads.