If i start on a new realms, I am farming a lot of transmog from classic and Burning Crusade Dungeons and Raids. In the beginning, i start to post them if they have at least a DBRegionMarketAvg (Average value of an item on all EU realms of the last 14 days) of 500 Gold. All the other items get vendored. The time you hit a stock of 1000 Items, my value treshold raises to around 2.500 Gold. All the items below that value get vendored aswell. Newly farmed items that are above these treshold will be listed. Why? If I start over somewhere, I want to get a certain amount of gold quickly. Cheap items are great for that. Later on, to save time, Quality is better than quantity. As mentioned above, re-posting the items on the auction house takes quite a bit of time. At this point, I can recommend you the TradeSkillMaster AddOn, it makes your auction house work really a hell of a lot easier.
Level with a pet if you can because it will help keep you safe. If your pet is tanking all of the damage from the enemies you’re fighting, you won’t have to. The other reason is that pets are easier and cheaper to heal than you are. If you don’t have a pet, make sure you know how to use your defensive abilities. You can’t level quickly if you are dying all the time.

Once you reach 575 you can purchase vendor recipes for the last 25 points. The Blacksmithing recipes are on a vendor in Vale of Eternal Blossoms. You can enter Vale of Eternal Blossoms after completing the questA Celestial Experience (requires level 87). After you completed the quest, you can find Jorunga Stonehoof (Horde) in Shrine of Two Moons and Cullen Hammerbrow (Alliance) in Shrine of Seven Stars.

Be aware of the seasonality of items. Check what items are used in seasonal achievements, such as Delicious Chocolate Cake or Small Egg during Children's Week. When the Darkmoon Faire is in season, Darkmoon cards and decks (Furies, Elementals, Lunacy, etc.) tend to sell well, but prices also tend to get depressed. When the Faire leaves, prices return to normal, but sales volume decreases. The same is true of things like Snowman kits, Red Holiday wear, etc. Holding onto that Snowman kit for a few months, and then listing it in July, can net you a significant profit.
You will need to cover very large areas in order to get a few chests as they are quite rare. Vanilla, TBC and WotLK zones work best. The way I like to do it is to park one Rogue class trial in Outland and one in Northrend, then fly over the whole continent and look for chests. One whole run might only yield 3-10 chests but you will still make a bunch of gold as you are almost guaranteed rares in chests in these zones.