Download... auctioneer... from www.auctioneeraddon.com

In the morning, while getting ready for work, and in the evening while getting ready for bed... run auction scans.
You're basically building your database.

Create an auction toon, that will never leave the auction house, except to visit the mail box.

Your mains will mail their stuff to the auction toon who will "Batch Post" the items.

To use this feature of auctioneer, click on the appraiser tab at the bottom.
Items are listed on the left. Click on each in turn, and then on the right check the "Enable Batch Posting" and "Enable Price matching" options.
Set the default auction time to 48 hours.
Once an item is set, auctioneer will remember your choices for it.

Get a mail addon such as CT Mail Mod.
This will allow you to open everything in your mailbox, without needing to manually click on everything.

I've found, roughly 50% of the items I list end up selling after 3-4 listings, but 50% do not sell.
The stuff that does not sell, mail to whichever of your toons is the Enchanter.
Disenchant periodically, maybe on Thursday, anything that has expired and not sold.
Then either save the mats for your enchanting skill, or auction the mats.

Just selling the cloth and green's from instances, or rare blue's, and leather (the only gathering skill I've bothered with so far)...
My shaman team was around 500g in week one and 800g in week two; they're 63 now and letting the hunter team level.
One of my hunters has skinning, so that team is leveling slower, but is making more. I believe 1100g range after a couple of weeks of playing them, they're 48 now.

Alternatively, you can use auctioneer to play the auction house.
This can make you a lot of gold, but has a bit of risks as well.
If you want to do this, you'll need "Classic Auctioneer" as well as the new one; you can download them as a bundle.

After scanning the AH morning and evening for at least a week, ie 10-15 scans, your database is sufficient to start.
On the "Search Tab", select Buy-Outs, with a minimum profit of 50 silver and a Percent Less of 30.
Click search.
It will find items, from your most recent scan.. where the buyout is 30 percent or more below the average scanned value, and where the profit is at least 50 silver.
You can tweak these numbers, but a small profit on a lot of items is very little risk per item.
I'd not buy anything, unless your scan data shows you've seen it at least 20 times, 50 is safer.
People do try to scam others by listing 20 of a worthless item for 500g each, and then a week later listing the same item for the bargain price of only 73 gold.
Use common sense, don't buy anything of grey quality.

I've personally moved away from the scan-buy-resell approach, as it just took too much time.
I was consistently making 200-300g a day, based off of one scan in the evening.
I was also spending 45 minutes to an hour on my auction activity, which wasn't all that fun.
Over the summer this year, with very limited online time, just running auctioneer... I purchased three epic flyers.
So the money is there, if you want this method. But it will cost you time.

Even if you're only selling what you loot while leveling, auctioneer will supplement your income by a large amount.
Hopefully something here is useful to you.