I'm using Quick Auctions 2, for my gem efforts.

I click the cancel button, which cancels any auction in which I'm not the lowest priced seller... provided it can relist the gem and still be within my minimum to maximum sale range.

I then empty the mailbox of gems, head back to the auctioneer npc, and click the Post button. This will post gems at 1 copper (my configured undercut value) below anyone else who is also selling gems. If no one is listing a particular gem, it lists at my maximum value... and will use the maximum value as my list price, if the market is currently below my minimum value. Also, I have it configured to go as much as 25% over my maximum value, if the lowest price is higher then my maximum.

After doing this, I click Summary. Then choose the Gem tab, and click Get Data. This scans every type of gem and gem produced item on the AH, giving me: a) How many I am listing (in green if I have the lowest price, in red if someone is selling for less then me), b) How many are listed in total, and c) What the current lowest price is for that gem type.

Anything I can make, which is selling for enough that I'm happy with the profit, I cut if I'm not listing that type of item.
Then I hit Post.

Between battlegrounds, heroics or just periodically when I'm leveling toons... I log off the toon in Slot 2, logging my auction toon on. Hit cancel, empty the mail box, click auctions to see what has sold, cut a replacement for anything which sold, then hit Post.