Zeni Management

Maximizing units can be a very big strain on zeni, so you'll want to be conservative with your spending. You start with a significant amount of zeni, but you will burn through it quickly if you're not careful. Note that ingots (i.e. rainbow, gold, silver and bronze) are converted to zeni and have no other purpose.

Early Game Zeni Tips

 * Take full advantage of the beginner shop (you have access for 7 days). Although this will result in you spending a lot of initial zeni, the discounts on items are significant and will likely save you zeni in the longer term. It's worth buying all the items available for zeni.
 * Don't try to raise too many units at once- focus on getting one good set of 4 or so units up to start with before raising more.
 * Before raising skills all the way to 20, you should verify that the skill is one that you'll want to use. For some units that you can farm to 2nd job pretty quickly, you may want to skip over some skills because they will not be used once you unlock the 2nd job. For your tutorial unit, if they have a job upgrade available for their main job, just raise enough skills to get by until you can upgrade the job, because you will have to raise them again after the upgrade. Raise counter skills last, as most aren't as critical to unit performance as other skills. Also, some skills do not get better with more points- some examples are counter snipe, cross counter, and clock resist. If you are planning to do a job upgrade soon for a unit, you should raise only the minimum number of skills required to get by until you can apply it. You can also read some tips about Ability Leveling.
 * Enhancing equipment is very expensive. Never do it before job level 11, only do it on the main job for a unit, and don't do it except for units you use very heavily. If you plan to do a job upgrade for the unit, wait until after you do it to enhance that equipment. The small stat gain comes at a very large cost.

Zeni Acquisition

 * Gold Rush is available every day. You should do all 4 versions as it costs no AP. You can also occasionally acquire gold keys from various rewards, which allow you to unlock Gold Rush for an additional run.
 * Each hard quest rewards at least 1 gold ingot for completing it without items. In chapter 1 the number of ingots scales per episode. Chapter 2 is only one ingot each. Chapter 3 is 1 ingot until episode 3 at which point it rises to 3. It's best to do hard quests you haven't completed during half AP events, but if you are short on gold you can do them at any point.
 * The daily milestones reward some gold ingots, so you should do those every day.
 * Event quests often have rewards of ingots either from quest missions or milestones. Occasionally events will also drop ingots. Some events come with special daily quests for additional ingots.
 * Mystic Tower Veda and Mystic World Mobius when available gives some zeni for each floor cleared.
 * Consecrated Elements runs monthly for 2 weeks, and if you do each day's quest, you get keys you can use to unlock a bonus quest which gives a lot of rainbow ingots.
 * Ingots are given for some of the daily login bonuses, as well as sometimes for event specific login rewards or challenge boards.
 * Some coin exchange shops sell ingots in exchange for special coins- usually these are not good uses of the coins but occasionally it can be a good option.
 * You can sell items you are sure you will never need (like shards of non-useful gear or extra equipment left over after applying a J+ upgrade) for zeni in the shops.
 * Some of the more expensive summon banners or bundles will give rewards of ingots - this is not a good reason to purchase these, but it's an added bonus.
 * During Phantom of the Alchemist reruns, you can use auto-repeat on the Phantom of the Alchemist III [EX 1 ] quest to obtain 55+ gold ingots per clear.