Making Gil

[Anapingofness]

There are some things you can do both at your current level and when you level up.

Starting with the stuff you can do right now~
Do level is your daily roulette. As you level up and unlock more content, more roulettes will become available to you.
Each roulette will have a gil bonus along the exp/tome bonus. ^^

Do side quests and story missions, picking the money prize (allagan coins)
Once you get higher up in levels as a miner you can mine up timeworn maps. They can generate 1.6k-5k gil a map.
Mind you, you can only gather them once every 18hrs but you can complete as many maps as you want.

You can also send your retainer out on ventures or alternatively, send them to mine stuff for you. They will bring in allagan coins as well as other misc stuff. Sometimes, that stuff will sell nice...other times... not so much lol. Just remember, your retainer can only level up to whatever level you have of that job. So for miner, it would be level 17. Furthermore, it can only gather stuff that you have gathered at least once. So if you get miner to level 50, your retainer's miner can go up to level 50.

At later levels are beastmen quests which all give gil as a part of their rewards.

Another option is to do your leves. They accrue slowly but if you let them build up some, you can blow through them to level miner or a craft, or even a DoW/DoM class you can make a pretty penny. Even without exp reward they will still drop gil.

Lastly, try and complete your challenge log. It gives a nice bonus of gil weekly.

A tip for using AH. Always check the sale history and try to monitor the market.
Prices will vary throughout the day so try not to undercut. Sometimes, it takes a bit longer for stuff to sell but imo it is worth the wait.
Finally, try not to flood the market with a particular item.

Hope this helps!