Making Gold in World of Warcraft
Nine Common Mistakes

If you are making any of these mistakes fix them and you will start making a lot more gold.  You can get your mounts, better gear, etc.  This guide is really written for level 70's, but most of it applies for lower levels, too.

Common Mistake #1: Not Saving Money
If you are not saving money, then that is why you never have any!  Don't spend much money on gear at the lower levels, you should be saving, and you will get better gear from quests and instances.  Don't spend money on anything you don't have to, basically.

If I don't have 500 to 1000 gold freely available, then I consider myself low on funds.  Choose a lowest acceptable gold level, and when you fall under that, your number one priority should be to make gold.  And then DON'T SPEND IT FOOLISHLY!

Save up for your next mount plus an extra 500 or so gold, is my recommendation.  If this is too hard for you, try sending the money to an alt, so you don't see it in your face and spend it.  If that still doesn't work, you could try sending it to a trusted friend to hold for you.

By the time you have a character leveled, you should have plenty of gold just from the quests you did to level, unless you foolishly spent it.  And there is your faster flying mount.  

Common Mistake #2: Not using the Auction House
If you want to make gold, you need the AH.  Learn how to use it, it is no big deal.  While you are standing around and saying "wts 3 primal fires pst", you could be out making more gold!  Instead, put them up on the AH and go back have more fun and make more gold.

Common Mistake #3: No Auction Alt.
You should have an auction alt -- a level one character that is always in a major city -- hanging by a mailbox and an AH (auction house).  You send stuff to sell to your alt, who takes care of it for you.  That way, you can empty your bags at any mailbox.  This is a very time efficient way to make money; you don't need to go flying to a major city to use the AH! 

Common Mistake #4: Not Disenchanting Greens
When you disenchant (DE) magical items, they produce enchanting materials, which people will pay well for.  I make sure my main or an alt can DE everything. If you don't have an alt that can DE your stuff, find a friend who will do it for you.  This is worth way more than vendoring the items.  Most greens and even most blues,  don't sell on the AH -- unless they are twink items -- because smart players know not to pay for gear off the AH as the norm, they get it from questing, instances, raids, and crafting.

Common Mistake #5: Not Picking Everything Up
Pick up everything that drops!   When your bags get full, fly over to the nearest mailbox and vendor and empty your bags.  Greys get vendored, and it can add up to a lot of gold.  Gathered items and any rep items get sent to your auction alt.  Greens go to your de'er for disenchanting then from there to your auction alt.  Note that this implies you have lots of bag space.  Bag space is worth investing in -- get the biggest bags you can afford.  Get them crafted by a guildie or pay for them off the AH or from vendors.

Common Mistake #6: Not Gathering
My main is an herbalist, and my first alt is a skinner.  The gathering professions (herbalism, mining, and skinning), make ridiculous money.  You should have at least one, and possibly both, of these professions if your purpose for picking professions is money.  The Gatherer addon is awesome for these professions, get it and use it. 

Common Mistake #7: Not doing dailies
Daily quests are very easy, and you make lots of gold in not much time. Plus, it helps you get rep.   For more on daily quests, see:
WowWiki Daily Quests Article

Common Mistake #8: Not questing for gold
Assuming you are already leveled up, you can quest for gold.  Get all the solo quests done, and save that money.  Hook up with friends to get the group ones done, and you'll all make that gold, too.

Common Mistake #9: Not farming
Anyone can farm for gold.  Most primals or [whatever name they are using for them in Cataclysm] sell for a lot of gold a stack on most servers.  So find a good place to farm them, and get to work! 

Conclusion
Gold is really easy in World of Warcraft.  You can have all the gold you need via gathering, the dailies, farming, and questing, selling what you pick up in a smart way, and not being stupid about how you spend the money you make, you can have your epic mount and a lot of really great crafted gear, no problem.

I intentionally haven't included a lot of specific tips and tricks -- hell, there are dozens of tricks to make money.  But the real money is via my nine principles listed above.

If you are lower level, you can't farm primals or do daily quests, but you can still do most of what is suggested above.  Have fun!