As I think about this question... You can earn merit by doing these following things..

1  Don't think about earn merit just do your job..
2  Do research before posting anything on the forum.
3  if you have good knowledge of the forum subject then your post quality is also good.
4  for making good quality posts you have to read and research on the blockchain technology, btc, Bitcointalk forum etc..
5  after doing all this things just give your best for the forum.. Always be helpful for others. Follow the rules and regulations of the forum..

If you doing that way then other members give you merit for your post too...
In one statement I can say..
The more you doing efforts for your post quality the more you get merit...