Simply public sharing your opinion about various subjects will rarely result in merit. Redundant posting (answering a question that's already been answered, without adding anything new) will also usually not result in merit. In my experience, genuine attempts to either acquire or dispense knowledge, usually attract merit (depending on how interesting it is and how much effort was made). Obviously, there are many other ways (like humor in appropriate threads, finding and reporting plagiarism, etc.), but I think those first two are the most reliable.

(Thank you)