It's simple but need time. Writing constructive, creative, high-quality posts, then you will get merits sooner or later. The most important things is be helpful in the forum to help others solve their problems, or at least give them hints, links for more details, etc. Furthermore, merits will be given for high quality posts, but it's also a game of probability. Therefore, you should not pay too much attention on merits, just keep being helpful, you will get merits in the future for sure. Don't worry about merit points.