To play a slower game you need to impede your opponents progress. Cards like Spiritomb AR and Mr. Mime MT are becoming very commonly used as walls. Spiritomb prevents the playing of trainers while active, and Mr. Mime forces your opponent to either remove him from the active spot (Bright Look, Warp Point, Poke-Blower+, Pokemon Reversal, etc.) to do damage to the active Pokemon, or lay down at least 3 energy cards to KO Mime.
There are ways around both, but if you build the right list it can make it a lot harder to get around the wall.
Quick setup is a key in about 99% of the most viable decks out there. If you can effectively slow down your opponent's setup while not impeding your own badly, then your options open up a lot more. things like Tyranitar that, while they can be run with speed in mind, still can never catch up to a deck doing 90 for 0 on turn 2 have a chance again.
Try some things that are maybe a little more rogue and see what you can come up with.
