It's all about balance
The more you sell, the more you have to craft. The more you craft, the more you have to mill. Milling is as boring as sin, and unless you cheat and use some hack to break the terms of service, you're going to be pressing your mill button a lot. There are ways to increase your efficiency and reduce the mindnumbingness (more on that in my next post); however, no matter what, milling time will be a limiting factor.
The type of business you run will determine how much you sell. You will need to find your comfort zone between the competing forces of profit margin and volume.
Profits vs. volume
Silly Basil -- profits and volume don't compete! Yes, they do. The higher your prices (and hopefully profits), the less likely a buyer is to want to buy a glyph. They could buy the mats and get a friend or trade chat scribe to make it, they could hold off for now and assume that prices will go down soon, or they could just get a cheaper glyph. The cheaper the glyph is, the more likely they are to skip the hassle and buy it. This means the lower your prices, the more glyphs will be sold. Somewhere between so expensive that nobody ever buys anything and so cheap that instead of spending three hours a day milling, I should spend it leveling another trade skill and use it to make 6,000 gold per hour, you will find your sweet spot. The more people looking for one, though, the less you'll each make.
Another factor you'll need to consider is how likely your competition is to craft a glyph. On my realm, I can post a bunch glyphs just under their 300g price and without fail, within minutes, I'll be undercut. I've got no idea how often these high-profit glyphs sell, because I'm not willing to look at my glyph mule alts more than once every 48 hours. All I know is that the prices are still 300g (well, 299.87g, actually) when I come back, and I don't get a single sale. On the other hand, when I post a bunch of glyphs at 60g (which is still about 40g profit), I sell a ton.
In order for glyphs to settle into a place where they're selling fast enough to satisfy all the people trying to sell them, you need to do more than undercut by a copper. The more you undercut, the less likely you are to get undercut back and the more demand there will be for the glyph.
Since I am on a two-day repost cycle, I tend to undercut by about 10%. Over the course of a week, I'll drive a glyph being posted at 300g down to the point that it sells enough that my stock gets bought out as quickly as I put them out for sale. This strategy annoys those of my competitors who rely on camping to remain on top of the heap. They sometimes buy out my "underpriced" glyphs and relist them, and they often send me angry letters.
The camping strategy
Ah, campers. Camping is the strategy of being present as frequently as possible, so you can relist your glyphs right below whoever just undercut you. Since the price is not significantly changing, campers compete by outstaring each other. Whoever can keep their eyes glued on the screen for more hours in a day gets the most sales.
The way I deal with campers is to keep undercutting until I push the prices down to the point that the demand is high enough that I still make sales. Also, low prices make undercutting feel like a waste of time (which it really was the whole time) and encourage them to use that time on more profitable things.
Of course, your ability to keep prices low depends on your willingness to craft. If you're going to lower the prices from 300g to 60g, you need to be willing to mill enough herbs to keep all your glyphs in stock, and the more campers who leave for greener pastures, the higher your sales volume will get. If you can't keep up with it, you'll find average glyph prices creep back up, which is exactly what's supposed to happen when the balance of demand and supply is changed.
Breaking into the market
Breaking into the glyph market is never easy. You're going to encounter stiff resistance, and it may come down to a game of chicken. It's tons of fun, though, and there's tons of money to be made.
The first thing to expect is that your competition will step up their camping efforts when they notice a new (serious) entrant. You have a few ways to deal with this. Resetting the prices down way below their former levels (but still above cost) is the easiest one and has a side benefit that some of the competitors may elect to "buy you out" and relist. Of course, you're now making as much money as you have time to craft, until they run out of money or realize you're not disappearing.
Not disappearing is actually the key to success. You need to find a level of activity (crafting, posting, and relisting) that you can sustain, and do it for months. You are either entering a fat enough market that nobody stops posting glyphs even though you're taking a share of their profits, or you're going to have to outlast someone. Nobody will lose money in this competition, but eventually someone will break and give up the low profits per hour to find a new market. When this happens, profitability should return to the previous level, and your share of it will depend on how hard you're willing to work for it.
"This sounds stupid."
One thing you can do to break this addon- and competition-heavy mold is try to find a way to inject some value (convenience) into selling glyphs by offering complete class packages in trade. Most glyph sales are coming from new characters anyway, and instead of selling to them when they decide they want a glyph on the AH and you happen to be the cheapest, offer a complete package of all the glyphs for their class for a fixed fee. Players benefit by not having to shop for an hour and possibly spend more than half their money on 10% of the glyphs they'll need.
Maximize your profits with more advice from Gold Capped as well as the author's Call to Auction podcast. Do you have questions about selling, reselling and building your financial empire on the auction house? Basil is taking your questions at firstname.lastname@example.org.