To get Merits in this forum you have to contribute by helping others, have to follow forum rules and should share proper knowledge with everyone. When you will share or help someone forum Members will appreciate your contribution by sending merits. So it's really very easy to get merits but you have to be on the right way.
My suggestion is that don't focus on merit earning just write constructive and high quality posts and try to help others as much as you can the you will obviously be appreciated by a lot of merits.
Don't abuse merit system by trading or begging then you will be red tagged.

This would be helpful, read in details and understand

Merit & new rank requirements

To earn merit, make quality post. To make quality posts, read than you are posting, especially read what quality posters' topics and replies.