Trying to buy low and sell high is what your average person thinks of when they're told to work the AH for gold. This is obviously not true and will rarely get you anywhere as your sole source of income. However I have been doing this for the last couple days with some degree of success due to things changing with the patch. A lot of things are going up in value, others going down, but there is still a day to day desire fro these items so they will still sell for "normal" prices. One example is eternal fire.
These are used for a good number of things from cloth to titansteel which people are making every day, even some epic boe gear needs it which people still want. However with orbs buying the eternals in 3.3.3 their price will go down slightly. That means that people are selling what they have for a good price while they still can, making the price go down even further. Then once the prices bottom out a price spike comes since people still need them and they go back from 18g to 45g. Pay attention on your server and find what this is happening to and take advantage, you can easily triple your investment by having good timing with this.
Other things that are getting this effect are -saronite bars (and therefore titanium bars) due to the loss of titansteel cd -frostweave cloth, to make specialty cloth out of imbued -Eternal shadow and life -all enchanting mats (dust has spiked up to 60g/stack last night) -epic gems
So far the most consistent one is fires every 3 days and infinite dust every 4 days. Once that clock runs out the prices are either going way up or way down and I start to collect or stock up like mad. Give this a look on your server and see if you can pick up on any of these subtle happenings and make a few gold off of it.