Refer to this thread for the full 1-4th job guide. Note that the guide was written for pre-Chaos, post-Big Bang, so the 4th Job is slightly different (hence this new thread/guide).
Some things to note:
Spoiler!Early 4th Job builds widely vary from person to person. Depending on your preferential way of leveling, you may choose to get different skills at different times. Personally, I try to avoid having many different attacks and aim for simplicity. My builds derive from that principle. They aim to max the skills that deal the most damage at maximum level first, so that later levels are easier to obtain (somewhat).
However, others may feel differently and some like having a multitude of skills to train with. If you are one of these people, feel free to throw points wherever you'd like; by 200 it won't really matter, as long as you have your important skills maxed. An example is of people putting early (120-121) points into Wrath of the Octopi and Elemental Boost. The Octopi's attack speed greatly increases (from what I have read), and level 1 EB increases your damage on FT/IS by a significant amount (22%). Depending on where/how you train, they might be beneficial to raise early on.
Regarding Mastery Books:
Please note that the availability of Mastery Books depend on the server.
If you are in a busier server such as Scania or Bera, it will be very easy for you to locate your Mastery Books. However, in servers like Kradia or Dementhos, where populations are very low, it may be exceedingly difficult to find skill books.
In this case, I recommend you save up several points for when you do obtain the books, and begin putting SP into other skills.
None of your main training skills require you to "learn" the skill via Mastery Book (Ie, TripleThrow10 for Night Lords), and so you can go ahead and spend points into other skills while looking for Mastery Books.
I personally had difficulty finding Torpedo20/30 in particular, and so I saved 5 points (for level 15 Torpedo which hits 5 monsters) and put the rest into Cannon.
Finally, please remember these are general guidelines, not hard-and-fast builds. I would very honestly recommend you judge how/where you're going to train and allot skills according.
>Bossing (For Advanced/Experienced Players)
Spoiler!1 Torpedo, 1 Battleship, 1 BS Cannon
1 Airstrike, 1 Elemental Boost, 1 Octo
Max Cannon
Max Battleship
Max Bullseye
Max Revenge
Max MW
Max Torpedo
=> other skills
This is a build for people who want to go jump on Zak/Pap/Boss training ASAP. It's also pretty decent for Lionheart Castle, since there's a good chance you'll be 1v1'ing the monsters a lot, assuming you have 1 HS mule and a party of attackers, rather than multiple mules (HS, BaM, etc) and very few attackers.
Note the lack of Rapid Fire in the early build. Post Chaos, your ship does not break, and thus you will never use Rapid Fire, ever. Cannon out DPSs RF significantly, not to mention has a higher crit rate.
I do NOT recommend this build for newer players. The reasoning behind this is because it will rely heavily upon your ability to boss, and your gear. If your Corsair is your first 4th jobber, chances are you are not well funded and do less damage than needed to train optimally on bosses. In this case, follow the General build below.
>General
Spoiler!1 Torpedo, 1 Battleship, 1 BS Cannon
1 Octo, 1 Elemental Boost, 1 Airstrike
Max Torpedo
Max Battleship
Max Battleship Cannon
Max Bullseye
Max Revenge
Max MW
=> Other skills
Note the lack of Rapid Fire in the early build. Post Chaos, your ship does not break, and thus you will never use Rapid Fire, ever. Cannon out DPSs RF significantly, not to mention has a higher crit rate.
This build will be very effective at LHC. Because most of the time you will be mobbing 2 or more monsters, max Torpedo (900% x6 mobs) will out damage Cannon (300%x5 to 1 mob) most of the time. There's the added critical rate on Cannon, but in all realism, you will most likely be attacking 3-4 monsters 80% of the time.
Because your ship doesn't break post Chaos, I prefer to get more damage directly from skills than from the ATT boost the ship gives you. Ship is maxed second to boost your Torpedo damage output, then BSC for 1v1 damage. Next, Bullseye will significantly boost your Cannon damage and Pirate's Revenge will help your overall damage. You can max Pirate's Revenge before Cannon if you find you rarely use Cannon and are using Torp almost exclusively.