Some of the easiest ways is to play games, personally booty grab is my favorite.
Aquariums that have glowing fish inside them are able to be visited and a game will start allowing you to collect coins, if it's a good tank you can get a good lump sum of gold at a time.
if you are needing assisstance in getting started
i have a guild that accepts new gaians, and we would love to help you
just click the banner and it will take you there. (we are new so we are still small but we are growing)