The most important step in being able to buy a mount and make other large purchases should be self-evident: saving. Economize as often as you can, and don't buy anything unless you absolutely have to. You can burn through hundreds of gold even before level 20 by visiting the auction house for new equipment at every opportunity. If you do so, over the long haul you will be left with very little to show for it. Before level 20, keep your eyes on the prize: getting that mount. The mount helps you move faster. Faster movement means faster killing, faster questing, faster quest turn-ins, and faster leveling. It is the most important tool to fast leveling you can get at level 20, and infinitely more important than getting your hands on that Left-Handed Vorpal Cleaver of the Zipswitch that you could have purchased at level 23. Stay focused.
That being said, there are occasions when a little kindness is not unwarranted. A typical example is a new player who just dinged level 20. They are suddenly confronted with a whole set of relatively expensive skills at his or her class trainer, and the cost of mount and riding training, and needs a small amount of money to learn those new skills. Likewise, sometimes one sees a player who, just by the way he or she walks, is clearly a new player. Kindness to non-whiny, well-intentioned, legitimately inquisitive newbies is karmically rewarding, and one should not worry about shelling out an occasional boon to such players. Remember, at that level, a few gold can go a long way. Heck, even a few older bags that you have lying around collecting dust in your vault will often be much appreciated.
Okay, speaking of pet farms this one is a really unique farm. What we're looking for is the carrier cage : black tabby. This is a very sought after pet for both horde and alliance – which is why its price competitively at 55,000g. The farm takes place in Hillsbrad Foothills on a peninsula like piece of land just northwest of the yeti caves. There will be dozens of stormpike engineers surrounding ballistas that only horde characters can kill. However, that doesn't mean alliance polayers can't do this farm (im alliance myself). All you need to do is to create a class trial (monk is the best) and send him over to the grinding spot. Use the black ox statue to attract the mobs, and easily maul them down group by group. If luck is on your side, you can make out with an awesome black tabby carrier.
It's hard to step out of the shadow of Legion, which was utterly fantastic in almost every way, to enter an expansion where you get one item per boss in the last expansion because the rules have been changed to force more grinding, where you have to grind reputation in the old expansion that you probably skipped because rep grinds suck JUST to unlock allied races (who aren't fully unique races since they recycle old content such as animations), where questing has SOMEHOW become boring again and where your new abilities are given by items you'll swap out every level, meanwhile being only boring passive effects no one cares about.
Rogues can make fast money from pickpocketing mobs, opening lockboxes and selling items that drop from those on the AH. If you don't have a rogue make one and get him to at least level 16. Rogues can also make some money by picking locks for people and getting tips. Not a great revenue source, but a decent one to supplement multiple strategies for making money. Generally, the usual lockpicking tip is between 50s to 1 gold, the most common being 50 silver. Sometimes, you can get lucky and have someone tip up to 5 gold for lockpicking several (or even just one) boxes. It's always beneficial for a rogue spending time doing repairing, training, etc. in a city to put up a lockpicking advertisement on the trade channel. Just make sure you let the buyers decide the price and that your lockpicking level is high enough.
Inscription is a very strong gold making profession. It utilises herbs and turn them into pigments for inks. The main outputs are glyphs that give cosmetic effects for your character. You can also craft trinkets that are upgradable with obliterum and Tome of The Tranquil Mind. As with Jewelcrafting you can make gold just by milling herbs. The glyphs are generally profitable, even though competition is usually high. The Darkmoon Deck trinkets have been amazing and so can Tome of the Tranquil Mind be.
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.