There are so many campaign going on related to the Merit, and that can be the easy way to earn merit. If you know about those campaign than please do share the merit.
I think that merit is not an easy way to earn,unless you are a good poster and useful massage.
I think also by getting merit is be patience.Time will come you have it.
I do not think for how long it takes to get merit and what is the criteria to say that you make a constructive post that capable for the merit. There are small number of people who share their merit to others, some are giving this because they know that person and ask for it.