Decoy as a buck, put it facing you. Bucks tend to approach other bucks from the front, to stare them down as a dominance thing. Every video of a buck approaching a buck decoy has confirmed this.

Decoy as a doe, put it facing away from you. Buck's want to get downwind to check her out.

It's best to put any scent you use on the ground, or better yet a scent wick hung on a stick under the decoy. Keep your decoys as scent free as possible.