Make minds until you are lv33 rc, and then make as many airs as you can. Sell some of them and use the money to buy minds. Then use whatever spell you please (fire/earth strike). Since you make more airs per trip, selling them at around 12gp will still make lots of money, enough to get a decent amount of minds. And whenever you need minds just craft airs, especially when you are over lv44 rc. Hope that helps. Also, try to train on monsters that drop runes such as natures, laws, chaos or minds. You can use them to boost ur mage lv as well!