This is meant to help you out, not criticize. How much you are in game is largely irrelevant if you're not being productive with the time. I'm going to assume you are being productive doing things that aren't netting you much gil- so I want to help give you some options.
If your goal is sincerely to really make money, and you've never seen more than 3m in a year, then let me suggest some things:
1) Most importantly, cut your frivolous spending. You don't need the latest fashions, nor do you need to buy any gear from the market board, at all. You can buy some filler spots to get you enough iLVL for the next dungeon, but you shouldn't be blasting your money on anything "current patch". It'll be there 2 months later, and by then there will probably be free alternatives via dungeons/raids.
2) Use your retainers more wisely if you aren't already: Do the daily 18 hour ones. These guarantee allagan coins (something like 3-4,000 gil worth per retainer per day). The actual drops they bring are mostly junk otherwise, but you might get lucky with a minion you can sell. This is an average 20-30k per week per retainer.
3) Trade in those allagan coins weekly to Doma. This is a solid 20,000k profit per week. for minimal work.
--These 3 are the absolute minimum you could be making, and require at most..15 minutes of time, per day. If you have more time to dedicate to gil, see below:--
4) Find a high selling leve to trade in (like coffee biscuits)
5) Sell in-demand resources like Treasure Maps, or materials that are currently used for the newest fashions. Whatever is current usually sells.
6) Engage in good 'ol market flipping. There are often things on the board that you can make and sell quickly (furnishings for example), or that are on sale on the board cheaper than NPCs will pay. Alternatively, there are things NPCs will sell for cheaper than the market board. You can buy from one and sell to the other with a hefty profit. I made my first million buying stuff like Candles in Limsa, or random crafting gear in the Black Shroud and selling on the market board way back in 2.0.
7) Literally just play the game. Do daily things like roulettes. Get weekly challenge bonuses. Play games at Gold Saucer.
8) Most time intensive: Level an alt to get retainers, then level that alt's fisher to 80 via Ocean Fishing, then level the alt's retainers to 80 fishermen. As long as a friend can unsync run you through dungeons you can trade the drops into ventures, or level the alt up enough to solo run for drops. 1 Gubal Library on my alt is enough for a week's worth of ventures.
It costs you zero extra money to have as many as 8 characters on the same server (if you pay 3 months at a time instead of monthly).
*Sidenote because you mentioned it: for retainers, setting them all to fishing is the easiest/best way to have retainers at 80 pumping out items with minimal equipment.. for me anyway.