Flipping is such a great way to make gold on the auction house but it is not noob friendly at all. You need to understand when items sell, why items sell, and where you should strike... that's quite a bit to ask of someone new to the game. With lots of experience however you can make flipping into a side business all by itself.
What do I mean when I say 'quick flip'? Well it means that I buy an item out for .8 * X price and I resell it within 1-4 hours for X + .10 * X price or more. The key is knowing that the item will sell fast enough. If you place the item up for 12 hour auction then you want it to sell fairly quickly and avoid getting into undercutting dilemas where a 48 hour auction would fair better. What items do I do this with? LOTS.
Here's a few major ones:
large brilliant shard
greater cosmic essence
greater eternal essence
eternal belt buckle
...and the list goes on and on.
Keep in mind that this strategy requires you to focus on items which sell crazy fast all day long or atleast during the time you are doing the quick flips. You want to get in, make a quick gold and then get out to allow the undercutters a chance to get the price back down to where you can buy and flip again.
Example: Large brilliant shards are going for 4 gold each and there are fifteen on the auction house for this price. I buy them all out and relist for 6 gold each. Within a few hours they all sell. That doesn't seem like much gold and it isn't, but when you do this with twenty different markets you make a decent amount of money. The trick is to automate this process with a snatch and batch post which will avoid wasting time on checking prices of each item individually with the standard search bar.
Here's a video I made showing where the snatch tool is located, which will help you with finding items to flip much faster: