First, let’s recap what a Mule is, what a Noob is, and what a Twink is.
A Mule is a low-level character sitting in your capital city. The Mule receives mail from your other characters containing goodies you’re going to put in the Auction House. The Mule auctions the items, and sends the gold back to the characters that need it (or the Mule buys the gear, weapons, recipes, and consumables and mails those to your higher level characters). Basically the Mule’s job is to save your main characters the time and trouble of having to go to your capital city.
A Twink is a lower-level character buffed up with the best gear and enchants for playing PVP battlegrounds. A Twink will be insanely powerful for his or her level. Twinks are always level x9: 19, 29, 39, or 49. (59 and 69 Twinks don’t make sense, since they’re so close to maximum level.)
If you have to ask what a Noob is, then you’re one. A Noob is a new, inexperienced player in World of Warcraft. Being called a Noob can be an insult. (You also can expect to be called a Noob if you are loudly wrong about something; for example, if you demand that a Warlock give you water and food, you’re going to be called a Noob, since Mages conjure water and food.) But Noob also simply means Rookie.
Each of you, the Noob, the Twink, and the Mule, have differing profession needs. Let’s take a look at these needs.
Noob
As a Noob, you’re going to need Gold! Leveling is your focus, professions are not that vital to you right now. But even a leveling Noob needs Gold. In many cases, a leveling Noob will do well to take two gathering professions, to focus on increasing your Gold amount, and because crafting professions take away time from leveling.
Later on, as you start leveling into your 50’s, you might want to drop a gathering profession and take up a crafting profession. The stuff you’re making in the higher levels of crafting can be worth having. But for focusing on leveling your first character, two gathering professions are the way to go.

Mining and Herbalism
An excellent gold-making combo for a leveling Noob is Mining and Herbalism. You can gather these resources as you go; as you level and quest out in the world. Gather them in bulk, then sell them in the Auction House (never vendor ore or herbs!).
Skinning and Mining or Herbalism
Skinning gives you the ability to loot some kills (beast kills) twice. You can loot the beast after you kill it, and then you can skin it. The skins will be in demand by leatherworkers, and a few other professions (such as engineering) that occasionally require leather.
You can occasionally really score with Skinning. If you find someone grinding on beasts who isn’t a leather worker, you can follow him around and skin his kills. You can pile up a good bunch of skins quickly when someone else is doing the heavy-lifting. Sell the skins in the Auction House.
Alchemy and Herbalism
If you want to take a crafting profession anyway, Alchemy is a great profession for a leveling Noob. The potions you make can save your bacon, and enable you to take on challenges above your level.
For example, Health and Mana potions can keep you up and going during a grinding session. Potions that increase your damage and increase your armor or health will be invaluable when taking on a boss. You can handle greater challenges when buffed by potions.
Now the downside to this is the potion bottles cost money, and you have to get trained (spending time and money). The upside to help balance this is that most potions will sell in the Auction House if you ever need extra Gold.

Secondary Professions
The secondary professions (First Aid, Cooking, and Fishing) are a lot of fun, but as you are leveling, only First Aid is worth having. Consider First Aid to be vital. Being able to bandage yourself after a big fight is better that sitting around waiting for your health to regenerate; First Aid saves you time.
Cooking and Fishing don’t contribute much to your leveling process. If you are in a hurry to level, ignore them for now. Later you can level them as high as you need.
Mules for Noobs
Even Noobs might consider rolling a Mule for your mail and Auction House needs. True, as a Noob, you’ll be visiting the capital city often for training and maybe an occasional battlegrounds run. But even you, the leveling Noob, can level quicker if you have a Mule to handle the business chores for you.
Twink
As a Twink, you’re a pampered, high-powered killer (or healer). Your job is to run the battlegrounds and destroy the enemy. Since when you’re not out killing things you sit back in your capital city sipping mint juleps and making passes at members of the opposite sex, you don’t have much need for a profession.
Or so it would seem. But that’s not the case.
A good Twink will have Engineering. Period. End of case. You can buy almost everything else you need, but Engineering is required to make and equip great head pieces, trinkets, and to use bombs and grenades and other such devices.
A great choice for second profession for a Twink is Jewellcrafting. You can make and equip rings and trinkets that non-Jewellcrafters can’t use. With Jewellcrafting and Engineering, you’ll have an advantage over Twinks without those professions.
Another good profession choice for a Twink is Alchemy. You can buy herbs in the Auction House and make your own potions.

As you can imagine, a Twink has absolutely zero need for a gathering profession. Twinks never venture into the world – they avoid any experience gains at all costs. A Twink is like a gigolo – some else pays the bills, and the Twink just performs.
Mule
Many times a Mule is a level one character. But there’s no style, no grace in that. Imagine your business agent, running around in rags in Ironforge or Orgrimmar. How can you live with such shame?
A good Mule will be higher level. Why, other than to look good? A good Mule will have the Enchanting skill. And you want our Mule to be high enough in level to be able to disenchant stuff you can’t or don’t want to sell.
A second profession for a Mule is mining. With mining the Mule can smelt bars of ore, and if you have a main character that is a Miner, he can send the Mule the ore rather than taking the time to smelt it himself. After smelting the ore, the Mule can then auction it.