There are 6 different crafting professions in Aion, and all 6 provide something valuable in their own right to those who know how to take advantage of them. The best way to approach the crafting process is to know ahead of time which profession will work for you and then to throw all of your energies into it, rather than trying to do three or four professions at once. It will allow you more control over your resources and also a better grip on the process of developing your stash of Kinah when you reach level 50.
• Alchemy – Alchemists will focus on crafting items like spellbooks, orbs, manastones and scrolls for casters. They also make potions for instance running. Those who are casters will benefit most here though, when you reach the higher levels and end-game content, you can get a tremendous boost by having this profession.
• Armorcrafting – Armorcrafters make Chain and Plate armor which benefits all Warriors and Chanters in the game. If you are one of those classes, this profession is for you. If you are any other class, you can still make Kinah with it, but only at the end game level most of the time.
• Cooking – Cooks will make food with stat boosts for end-game content. You will find that a good place to sell this is in the Abyss or near instance entrances.
• Handicrafting – Handicrafters make odds and ends including necklaces, earrings, and trinkets. They also make staves and bows. A lot of Kinah can be made here on those baubles.
• Tailoring – Tailors make the cloth gear in this game. Cloth wearing classes should consider this profession along with anyone interested in the long grind to 399 where they can sell them.
• Weaponsmithing – Weaponsmiths can make weapons for every class except for the Staff users. You'll be able to make a nice profit here once you reach Level 50 due to the high demand for this type of gear.
For those that choose properly and then market their crafts effectively, the prospect of the right profession can not only help them make Kinah, but save a great deal of it as well as they reach end-game content, where most crafts have the greatest impact.
Ultimately, make sure to choose a profession that will directly benefit your class as well as your play style. The end-game Kinah benefits are all going to come later but they are just as viable.