The main way to earn Denar is to sell rares (i.e. the rare minerals used as crafting materials in recipes). You get rares by either mining them or trading other stuff (like recipes, quest items, warrior stones, etc.) for them
Just a few tips:
Get to level 45-50 first before crafting. That way it will be a lot faster for you to get the materials you need (such as sewing needle, warrior stones, etc) and you won’t have to buy them.
Know the prices of the various rare materials (pure iron, ancient coin, pearl, etc.) and know that these prices tend to fall over time.
Watch the market (aka. Kong chat) to see which recipes are needed the most and fetch the most Denar. Level 30 armor recipes typically sell well because they’re a major pain to farm. Level 40 recipes seem to be all over the place because those bosses are the ones that get farmed repeatedly.