1) Have a main character and a new character
2) Start a new character
3) When you are given the adventure cupon give it to the person that gives you 50G for it
4) Go up to the guy at any AH that will transport the gil to another character
5) Then type in the name of your other character and put the 50G in the place where the gil goes
6) After doing all that repeat the process and you will have free gil
Sell 12x Crystals for gil at Auction Houses. You need to be wearing a signet for monsters to be able to drop crystals so make sure you have one first.
Kill goblins and sell their armor, you can make 250 - 500 gil each.