Another hugely under-appreciated tip is to watch where you spend your gold. I'm not here to tell you what to spend your money on, but focusing your buying power to achieve a bigger bang for your buck can involve forgoing things.
For example: let's say you want to collect combat mini-pets, mounts, level professions, and get into end-game PvE crafted gear. On a fixed budget, you may only be able to really do one of these things well. If you just spend your money as you get it on whatever you see first (without prioritizing), you'll feel like you did less than if you prioritized your goals and focused your attention and money on one. Maybe one that will help you achieve the other goals: leveling and reselling Minipets is expected to be a very good money-maker that you could use to subsidize, for example, raiding gear or crafting professions.
Farmed materials are worth way more in the beginning of an expansion than after a few weeks. If you have a miner, skinner, herbalist, or fisher, you'll be able to make as much money as you want with surprisingly little work for the first few weeks. Everyone will be needing gathered goods in massive quantity while they level their crafting professions, and even though a lot of people will be farming for themselves, there will be a huge amount of demand on the AH.
The trick is to find a price where everything you list gets sold in 48 hours. This price should not be the lowest price on the AH; in fact, you probably want to overcut instead of undercutting. Pick a price where you're lower than any really large batches posted, and ignore the really low auctions. They'll get bought out immediately. In fact, one perfectly legitimate plan I've seen work is to post all your stock at a very high price -- like 50% above average, and simply wait for someone vying for a realm first achievement or something to come in and clean out the AH.
If you have a crafting profession, resist the urge to farm for yourself. You will do well to completely separate the decision to farm from the decision to use farmed goods. If you decide to use herbs, ore, leather, or fish in the first month on your professions, remember that even if you farmed it yourself, you could have sold it for a lot of gold, which means it essentially "cost" you what you could have sold it for.
Think of it this way: you can farm 30 stacks of leather on week one and use it to level your leatherworker part-way to the new cap. Or you could sell those stacks, hold the gold for 4 weeks, and buy 50, maybe even 100 stacks with it once the price goes down. There's a huge incentive for you to farm early and craft later.
Getting from level 80 to level 85 made me almost 10k gold, without touching the AH. Quest rewards, vendoring trash, selling cloth on the AH, and disenchanting or vendoring unused quest reqards played a huge part of that. Playing the game is something that generates a lot of gold, and since all these sources are inflated every expansion, you can expect even larger sums getting to 90. Many people don't notice these gains because they spend it as fast as they earn it, but it's there.
Additionally, playing the game will generate Spirits of Harmony, which can be used for personal profit by granting additional profession cooldowns or materials once you do get a crafting profession maxed. These items are random drops from killing things, and are not tradable.
The Tillers are a new faction that will allow you to keep your own little farm that you can collect goodies from. One of the plants you can plant is the Songbell Seed, which will allow you to harvest a Mote of Harmony (a ninth of a Spirit of Harmony) a day from it. If you have the means to turn those motes into gold with a max level crafting profession, 16 motes a day at exalted (with The Tillers) will be a significant amount of gold.
You should start doing reputation building activities as soon as possible, because most of the really awesome stuff players can craft is going to be sold by faction vendors to players with a high reputation.
Maximize your profits with advice from Gold Capped. Want to know the very best ways to earn 10,000 gold? Top gold making strategies for auctioneers? How about how to reach 1 million gold -- or how one player got there and then gave it all away? Fox and Basil are taking your questions at firstname.lastname@example.org and email@example.com.