The quickest way to make money is via the Hunter job. If you do /jobs browse and right click on the bow icon you will automatically join the job. Hunters make money by killing mobs, so if you find a monster spawner you can stand around and kill the mobs that come out to make money quickly. You can also join a town and some of the bigger ones have community grinders for residents to use.
I know this answer, essentially, has already been said, but maybe you need a second opinion to get you into action!
I personally use the ‘Hunter’ Job. You can join this by using the command /Jobs join Hunter.
If you go to Opportunity- (/t spawn opportunity’) or Brinta’s grinder- (/t spawn oasis) you can find some great places to grind.
Some anti-afk measures have been taken, so don’t immediately walk away! Keep killing monsters and making mad cash!