First off, I would use a supportive bra that brings the girls together nicely, but doesn't spill them out over top of your shirts. That is the key to nice and noticeable cleavage. For shirts, I would wear V-Necks, but not the deeply plunging V-Necks. Moderately plunging will be plenty. After all, save some mystery for the guys to get intrigued over. Remember, you are out to advertise the the goods for sale, not give them all away up front.