As a crafter I'm far from hardcore. Still, I was able to save up for and buy a house, when they first became available to individual players, and I'm sitting on more than a hundred fifty million after five years of play. Here's some tips:
- Level all the crafting and gathering jobs.
- Never buy mats, if you can reasonably gather them yourself. If sold cheaply by NPC (like Steel Ingots from the Ash tribe), this is also acceptable.
- Keep a stock of common crafting materials on your retainers for this purpose - NQ only, don't bother to store HQ, sell those instead.
- Never buy equipment, if you can reasonably craft it yourself.
- If a dungeon drop can be refined, crafted, and sold, do so - don't just sell the drop straight (e.g., if you get a Cracked Shepard's Belt on a Qarn run, lot it, craft it into a Vintage Shepard's Belt and then sell it. Don't NPC those Clear Prisms, craft them into Glamour Prisms and sell them), and certainly don't NPC it. These items may not sell for a mint, but they're generally in high demand and will earn you plenty over time.

Note that a lot of these tips exchange time for gil. It's way faster to buy a mat or piece of gear than it is to go out, gather the goods, and craft it yourself. If you don't have a lot of free time to spare, they likely won't do a lot for you. Crafting profitably can be a time-intensive process.