Ask a Magician Thread.

Here's an old build for your reference. I don't know what the new build looks like. Caveat: there is no "correct" build. there is only your own.

5 Improving MP Recovery
10 Improving Max MP Increase
1 Energy Bolt
20 Magic Claw
20 Magic Guard
11 Improving MP Recovery

no need to put 1 in energy bolt at the very beginning since the beginner's snail shell skill doesnt use up actual ETC items anymore.

1 Teleport
30 Heal
20 Bless
19 Teleport
20 Invincible
20 MP Eater
Rest into Holy Arrow

Bless and Teleport can be switched around depending on how much you PQ. I'm a big, big fan of Teleport, and if I ever made another Cleric I would probably max Tele before I maxed Heal. But that's just me.

For shyts and giggles here's how I would imagine what the third job build looks like these days.

1 Door
30 HS
20 Dispel
30 SR
20 ER
19 Door
15 Dragon
Rest in Doom

SR and Dispel are probably interchangeable, depending on how often you boss. Max ER sooner if you train in Ludi. A lot sooner. Max door is awesome.

Fourth job advice: Up til now, you didn't have to worry about gear. Now, gear is pretty important, as the godlier your gear is, the less you will level up Genesis. The goal is to 2hko as soon as possible while keeping gen as low as possible. When you calculate that you'll have enough matk to 1hko with gen30, you then must pass gen20 and gen30 and max gen. I leveled my gen to 8 just so I could 100% 2hko at a really low level, and by 13x I already regretted it. This part might not be clear but whatever, sounds like you got a ways to go before you have to worry about 4th job. Oh and last thing, Bahamut is worthless.

You know what pre-requisites are?