If you’re using the dungeon finder, you cannot use this neat tip, but if you’re going out on a boost, or have found your own group, you can utilize this trick to get much better loot.
In some dungeons there are bosses that only are there at random. This is the case for Shadowfang Keep, where the boss Deathsworn drop the loot Phantom Armor or Haunting Blade, a very nice sword. (http://www.wowwiki.com/Deathsworn_Captain )
No need to go through most of the instance before knowing if he’s there or not.
When you enter the dungeon, you simply type /target deathsworn – if he’s there, you’ll see his icon pop up. If he’s not there, you can leave the dungeon, reset it, and enter again (max 5 times per hour). He would be there normally at least one of these times.