If you are looking for game guide about how to farm FFXIV Gil, this guide is definitely helpful for you. Some ways are for new player and some for skilled players. Some ways are just to sell items and some need to fight with monsters. No matter which way you want, you can find an appropriate way for you to get millions of FFXIV Gold efficiently.
If you have good items, you can sell crystal shards and some quality gear piece check for ones that require x5, x6, x0, or x1 level) and whatever special treasure your retainer brings back once in a blue moon as a combination. If you have abundant Myth tomestones, you can investigate the price to buy materials from Rowena on the market too. For selling items, you can sell some materials with your retainer for some hefty money and should be fine for now but I think you can go with the long term crafting if that works, logs and repeatable quests which are very appealing. Currently leveling mining and crafting ATM which DOL and DOH is worth investing in, cause you have gotten plenty of time to level.
If you are new player with Level 50, I suggest you unlock Crystal Tower which gives you 100 myths on one good run and drops LVL 80 gears. But if you want to grind myths, do daily roulettes and Dungeon like, Brayflox's Longstop (Hard), Halatali (Hard) and Lost Town of Amdapor(2.2 new dungeon). If you don’t farm by yourself, just buy cheap FFXIV Gil from ssegold.com.
Another efficient way is to do Wanderer's Palace till you reach the level for Chimera. Nowadays, the speed runners do Brayflox HM so only the 'book' ppl do WP. What you're looking for is 'Darklight' gear (LVL 70). Besides your regular AF armor should get you near Level 50 already. Enough for Chimera? Go to do them if you have not, plus it looks cute (and can be stored in the armoire once you find something better).
If you are patient, you can find a hole in the market, plug it, rake in the dosh. You should have a better understanding on what you can and can't do. For instance, on my server Mastercraft Demimateria is steadily rising, but I don't know if you have a DoH geared enough to get the items. Even then I don't know if you have desynth leveled to break the items apart. If you have, this way can give you a fair amount of FFXIV Gil in short time.
Also, you can complete quests to get fast Gil. Some low level HQ base materials like HQ Linen Yarn, HQ Mythril Ingots and HQ Iron Ignots are quite rewarding as many players don’t have time to gather and difficult to gain. Each of them cost a few thousands of FFXIV Gil and it just takes 30 mins or so to get one.
Let’s say Twinthread is an average of 5K per HQ item which costs 50K Gil in the bad for cheap/easy to gather materials (discounting the shards/Dark-Matter repairs). That's a tidy profit. I do this every week at some point, I scout out random base materials, check the cost/obtainment method and whether or not it's in demand then go for it. I can make upwards 200-400K a week easily depending on the effort I put into it.