There are relatively few avenues for selling your profession's wares. The first, and probably the most universal, is to create your trade goods and then list them on the auction house. This is a pretty common channel for selling trade goods. As such, there's more than a few techniques and arts to getting the most out of working the auction house. Check out Gold Capped, for example, to pick up a lot of great advice on how to work the AH.
The second way to sell your goods is via small-scale professions gathering. We talked a few weeks ago about how to get together a crafting bazaar. The advantage to a crafting bazaar is that you get a lot of exposure from a lot of people. If your event is fairly well attended, then you're going to get a lot of different customers cruising to buy crafting goods. It's especially advantageous to spend time working with a consumer in a bazaar environment, because you have face-to-face interaction during which you can try and upsell the client. You can check out all of their gear and enchants, and make recommendations for things they might want to purchase to improve their performance.
There's a middle ground between those two methods, however, and it combines a lot of the best traits of the crafting bazaar with the open, free market of the auction house. By advertising your profession on Trade, the official forums, and word of mouth, you can get in touch with prospective customers while still respecting and interacting with your server's overall economy. You get the chance to meet someone "face-to-face" (or, at least, whisper-to-whisper) and you get the same chance to review the gear that you would in the bazaar. However, you don't have to wait for a special location or particular time in order to meet those folks.
Considering how important word-of-mouth can be to growing a network of steady customers, we should take the time to review a few tips for advertising your profession.
I know, I may be stating something obvious. But if you can somehow manage to navigate and dodge all the Chuck Norris and murloc jokes, the Trade channel can be a decent place to advertise your profession. The down side is that you're going to have a few dozen other crafters who are also rocking the Trade channel. At least you can rest assured that people must find some success there, or else you wouldn't see anyone using the chat channel. Just be prepared for some off-topic discussion while you're trying to sell your goods.
Trade Channel sales come in two obvious varieties -- posts from people who are proactively looking to buy an item (WTB) and people who are looking to sell an item (WTS). While it's awesome to be able to hook up with someone looking to buy what you're selling, most of your commerce will happen while you're advertising your "WTS." That's because there's more people looking for their "best option" while shopping around, and that includes avenues other than Trade (such as guildies, the auction house) that will compete with you. There's not much use standing around hoping you just happen to have the exact thing someone's hoping to buy at the exact time.
The best way I've seen to use the Trade channel is to avoid falling into the trap of merely focusing on immediate sales. Instead, the idea is to start getting your names as a professions-master "out there." Don't focus on your spur-of-the-moment purchasers, though obviously take the opportunities as they present themselves.
Create a brief, fun macro to display your talents (and your skill list.) For example:
Dudeguy McDudicus: Master level Enchanter, with everything you need. I'm available evenings to custom create your enchanting; happy to meet you right outside Icecrown Citadel and setup your gear as soon as it drops! Friend me for service!
Hopefully, if you do your advertising right in Trade chat, someone will put you on their friends list, and look you up when there's work they need to get done.
Okay, the official forums can be kind of a mess. But most of the realm forums are actually relatively tame. They've certainly been taken over by the weeds of raiding guilds constantly recruiting and the ongoing tumult of local drama. But, there are still a lot of well-connected players who hit the forums.
It would be ideal for you to start your own thread. However, there are two dangers to doing so. First, if there's no reason for people to regularly update or post in your thread, it will quickly fall off the front page. (And you really shouldn't be that guy who bumps his own professions thread just to stay on the front page -- that's not going to do you any favors.) Second, many realm forums already have a "Professions" thread stickied to the top. You need to be unique, thorough, and current.
What I'd suggest is start your first post with a full listing of when you are available to perform your profession, how much you charge, and what your most popular recipes are. Then, every time you make a new sale or a new connection, post updates to the thread. Again, make sure it's relevant.
Treat this thread a little like your online storefront, and the additional posts work a little like your business's blog. Post about sales (yes, you can run a sale), new recipes, and if you're looking to buy materials. Your writing should be short and concise, but have enough content that people will click your link to look at it. Encourage your customers to post in your thread, so that you can interact with them there.
Networking is probably the most important tool in building your professions empire. If you're not simply running your goods through the free market auction house, your best option for regularly selling your products will be networking with other players.
Every time you make a sale through the Trade channel or through the official forums, take a note of the customer's name. A week or so later, drop them a brief note through in-game mail. Thank for them for their business, and just kind of check in to see if there's anything else you can help with. For the love of Light, don't turn into a stalker about it. Just gently, politely follow-up.
If you know another high-level crafter who carries product that you don't, feel free to put their name "out there" at the same time you're doing business. That person might return the favor for you, and you could find yourself reaping the good-karma reward.
The idea is to be a straight-shooting, helpful person. People appreciate someone who's trying to do a good job, and they'll come back to you for further business. You help them, you help your crafting friends, and you will ultimately help yourself.
Good business out there, folks.