For those who have made the realization that even the citizens of Eorzea have to make a living after they have started their path to become a hero among heroes. Gil will be needed to buy and occasionally repair equipments, buy buff-food, potions, and teleporting. But they are just so expensive.
So here are some ways on how you can buff up your bank balance. However, since every server is different, you'll still need to research which one is most feasible, as these are just rough pointers.
Quests
In these harsh environments, the lifeline of every adventurer that brings his first class up are quests. Not only do quests give you a freedom to choose another item, for example, the Allagan Pieces that can be exchanged for Gil, it also rewards you with Gil in itself. Whether you can get the equipment from the quest reward cheaper, you will have to check and compare with the Market Board first.
Challenge Log
By doing the quest "Rising to the Challenge", you will be able to unlock the Challenge Log when you reach level 15. Coming with a lot of monetary reward, the challenge log resets every week and will give you a lot of little challenges. If at level 50, you can complete all the challenges, that is equivalent to 50,000 Gil extra in your bank.
Crafting
Crafting is the ultimate gift that keeps giving.Uunless you farm everything needed for crafting yourself, it can be rather expensive, so players just stop levelling their crafters. It all pays in the end, nonetheless. Other starters will prefer them to get their own craft levelled more quickly, and it becomes a cinch the creation of low-level high-quality items.
Gathering
A no-brainer for all gamers, where all you do is sell items that you have picked up, or craft into possibly better-selling items, if you have the crafting class for it. However, remember to do your research on the Market Board.
Converting
This feature can get you quite a bit of cash although it is often overlooked. The equipment you wear will gain Spiritbond while you fight, craft, or gather. You will be able to convert the equipment to Materia if it reaches 100%, without the need to wear it anymore, of course. You can achieve very good prices on the market depending on the type of Materia you get.
Dungeons
Finishing a dungeon can also net you a nice sum of Gil and rare items to craft with, as an alternate to rewarding rare equipment. You will also gain Tomestomes when you reach level 50. The Tomestones you can exchange for crafting materials that can sell very well which are rather pricey.
Market Board
Without ever leaving the safety of the city, some players are able to make a fortune. They buy low and sell high by observing the ebb and flow of prices when they spend their time with the Market Board.