The professions in the World of Warcraft come in two types. The primary professions, of which you can have only two; and the secondary professions, all of which you can learn. The professions cover everything from gathering raw materials to crafting epic items that are close to the best items in the game.
The Gathering Professions
These are the skills that you use to gather up raw materials usable by the other professions. The skills are mining, herbalism, skinning, and fishing. The first three are actually considered to be primary skills and you can only take two of them, as with any other primary skills. Fishing is a secondary skill and you can take it along with all of the other secondaries.
As you’re starting out you should pick two of the gathering professions and skip the crafting professions for now, due to their expense. The gathering skills are great for making extra gold or for providing cheap materials for your own crafting.
If you take Mining as a profession, you can mine for copper and tin ores and then smelt them first, separately, into bars of copper and bars of tin. Smelting your ores will level your mining skill. As you level up a little further you can smelt the copper and tin bars together to make Bronze bars. These usually sell fairly well on the Auction House (AH.) Mining is great for those who intend to go into Blacksmithing later, especially those who wear mail or plate armor.
Skinning is a no-brainer, as you will be running around killing skinable mobs while questing or grinding. Skins sell well on the AH. And don't throw away those ruined leather scraps; leather workers will buy them and put three together to make a single piece of leather. Skinning is a good choice for Hunters, Rogues, and other leather wearing classes, as they can also pick up Leatherworking at some point and make their own armor/clothing. Herbalism is also a nice skill and herbs sell quite well to Alchemists and Scribes (Inscription.) Scribes, especially, will go through a lot of herbs to make their inks, so there is always a demand for those herbs you will be picking.
The Primary Professions
Once you have reached a higher level you may want to select one or two of the Main Professions and drop one or two of your Gathering Professions. The Main Professions include: Alchemy, Blacksmithing, Enchanting, Engineering, Inscription, Jewelcrafting, Leatherworking, and Tailoring. These are better choices for higher levels due to the costs involved in practicing them. You need to build up your stash of money first, since these skills range from very to extremely expensive to level.
As you level your professions, remember to keep an eye on your skill level and to train up your skills when you can. Just as Class Trainers, Profession Trainers are not available in all towns, though they are available in all of the big cities. You might want to think about this and take care of it at the same time that you train your class skills.
Think about why you want to have these professions. Do you want to make money? Do you want to craft plate, chain, leather, or cloth armor? Do you want to enchant weapons, armor, etc?
If you are a class that wears mail or plate armor, such as Paladins and Warriors, Blacksmithing allows you to make mail and plate armor. Tailors can make cloth armor, which is great for mages, warlocks, and priests. Leatherworkers make leather armor worn by Hunters, Druids, Shamen, and Rogues. You can also make items for your other characters or sell items to others on the AH.
With enchanting, you can enchant weapons or armor for yourself and others. You will see Enchanters selling their skills in the Trade chat in the larger cities. Enchanting also allows you to disenchant items that you can’t use, resulting it enchanting materials you can use or sell on the AH.
All characters can level up the Secondary Professions: Archeology, Cooking, First Aid, and Fishing. But don’t overlook them, just because you can learn them all. These professions can be quite beneficial.
Cooking
Food that you make with the Cooking skill gives you back health lost in fighting mobs,. Some foods also give mana (used by spell-casters,) while others give increases to stats. One of the most important stats to staying alive is Stamina; increasing Stamina increases your HP (hit points.) There are several foods you can make that will increase Stamina. As you level up your cooking, you will learn new recipes that give ever increasing buffs to your stats. Some of these sell well on the AH.
Fishing
Everyone can fish, and it is best to level up Fishing as you journey from zone to zone. The game is designed so that you start in lower level zones and gradually work your way up to the higher ones. The required Fishing skill increases as the zone difficulty increases and if you skill isn’t high enough all you will catch is weeds.
Some of the rarer fish are used for various purposes in addition to Cooking and some sell well on the AH (Auction House.) Check the AH on your server to see what is selling well. You can use the fish you catch in recipes to level up your cooking and sell the rarer fish on the AH. You sometimes also catch chests and other items when fishing.
First Aid
First Aid teaches you to make bandages for healing after fights, a very good thing to have. It’s a good idea to level up your First Aid, even if you are a Paladin or other class with healing abilities. There will be times when you run out of the mana that allows you to heal, and then you will want to have bandages available to heal yourself or others. For classes that don't have healing spells the First Aid skill is pretty much essential.
The professions add an extra layer of fun to the game and the crafting professions are a good way to get rid of that extra gold that’s been bothering you. Actually, if you pay attention to the AH, your costs, and so on you can actually make gold with professions, not just spend it.