If you just want to make gil, that’s easy.

Take up crafting, the long and slow way of making everything at least once and only doing a Leve that you’ve made an item for. Sell everything not being used for a Leve, or for yourself (if there’s an item that’s both needed by a Leve, and that you want to use, make two! - four if its a Triple Leve).

Using Leves too much causes a gil drain. Making stuff and putting it on the board creates an income. Starting in the low-mid 20’s, you’ll be able to HQ fairly reliably, using entirely NQ mats, though this does entail having HQ gear and keeping it up to date.