On my server there's a big shortage of Primal Air. I've tried farming it in the past using supposedly the best spot(s), but it was honestly horrible. After looking at the Wowhead for Primal Air I noticed there's actually a transmute recipe for Primal Water to Air. I will say as a warning that it apparently does have a 1 day CD like a lot of transmutes, so for some people it might not be worth the time. But at least on my server, there's not 1 Primal Air on the AH and I know that it's a constant shortage, so at the moment I could make a lot of profit just doing my daily CD for this after getting the recipe. To get the recipe you do have to be revered with the Cenarion Expedition from TBC, and there's guides on Wowhead for grinding out that rep as well. I'd recommend checking the stock of Primal Air on The Undermine Journal for your server, and if it's relatively low and you have at least 1 alchemist, go for it. It could be a decent way of making a little more passive gold, just transmuting one Primal to another. I'm probably actually gonna start rolling another alchemist at some point, and this discovery has definitely prodded me in that direction as doing this transmute won't interfere with other TBC transmutes, because there aren't default TBC transmutes as far as I'm aware.
Be cold-blooded about admitting that you've taken a bath on an item. If you bought that sword for 5g, listed it for 10g, and the listing cost is 2g50s each time, after two times it had better sell just to break even. Once you hit that point, don't keep listing it over and over in desperation trying to make something off the AH. D/E it, or vendor it, and move on. Lesson learned. Don't get trapped in the fallacy of sunk costs.
As of Patch 2.3, if you get a message "Interface action failed because of an AddOn", this means that an AddOn interfered with the Blizzard UI in some way. To diagnose this, enter the following into chat "/console taintLog 1" and restart the game and try to reproduce it. If you reproduce it, you can quit the game and search through the file Logs\taint.log for the word "blocked" and mail the log to the author of the AddOn listed there. Once you have done this you can turn off logging by entering the following into chat "/console taintLog 0"
Bags: This SHOULD be a no-brainer. The cheap-o version are Netherweave bags, but if you have the gold I recommend you get the largest bags you can afford, since it means you won't have to stop to clean them out as often. In fact, if you have an excess of gold, it's probably not even worth your time to stop and loot mobs that aren't quest objectives. This seems like a small thing, but over the course of 100+ levels, all those clicks to loot add up.
I tell you my experience. I'm leveling a priest that it's 60 now and since I have also done some instances (and I have full heirloom set with 20% experience gain bonuses) and been very ahead of the guide, I skipped some zones since they were grey quest for me, well it was a real mess. Missing quests because I didn't to the previous to enable the following. Going in a zone then realizing that I couldn't do that quest because I didn't do the starting quest chain, very unconmfortable. In short what I suggest you it's not to skip areas, or make really sure that you do all the quests required (at least) and check carefully the previous zone you'll going to skip to make sure that you won't have problems with struggling finding where to start the quest chain to sync with the guide section.
EXCEPTION: If you are leveling trade skills while advancing, review the materials requirements of every recipe, pattern, plan, or formula that are planning on purchasing from a trainer. For example, some of the shirt patterns for tailors use very few materials and thus yield a more efficient manner of leveling the trade skill. Check profession leveling guides here on the wiki, ask a guild-mate or friend, or check out information on other web sites to help in this area. A little pre-planning and fore-thought can save you huge investment costs in the long run.
At 98 you have the option to drop what you're doing and return to your capitol city to start the quest for your Legion Artifact weapon. However, I do not believe this is necessary to do right away unless you're struggling with kill speed in your current gear. I would recommend waiting for a natural pause, such as hearthing to repair and clear your bags. From 100 to 107 you won't even really fight mobs that often; only just enough to clear the way to any treasure you need to pick up.
Gold for riding training. Travel time is a SIGNIFICANT time sink while using quests to level. You don't want to wait to get it. In fact, while questing, the second you ding 40/60/70/80 you'll want to hearth and train it IMMEDIATELY! 10304 gold is the base cost, which will be modified by reputation. Also, make sure you're in a guild with the 10% riding speed bonus unless you're a class that already gets a mount-speed buff.
Most of the players make the mistake of only listing 30-50 transmog items on the auction house and then hoping to get half of them sold until the next day. Me and a lot of other gold farmers and transmog sellers do have 3.000-10.000 items on the auction house across various realms. It does not mean you have to do it that way – but if you have 1000 items listed, chances are higher you can sell up to 10 per day. With only 100 items listed, you have to be lucky to sell one. Of course, the sells are not guaranteed if you post more items. But i’m sure you have a lot more fun if you open your mailbox and 10-20 items are sold