It's just a deck that's designed to get creatures/minions out really fast, and do a lot of a damage. Most decks like that are filled with 1/2/3 mana creatures, so you can play something every turn and you ignore what your opponent has on the board in favor of hitting them in the face. EDIT: For example, the hunter one typically uses haunted creepers, abusive sergeant, worgen infiltrator, etc.
I typically have no problem going from like 23 to 20, then early in the season I hover around rank 19/20. The highest I usually get is to about 15/16, and that's by being a cheese and using a rush hunter. >_>