Get In Sync
Sense the rise and fall of your own breath and your partner's, either by feel (if your backs are touching, for instance) or by sight. Take a moment of quiet before you enter into a pose to let your breath fall into rhythm with your partner's to calm and ground you.
Look Your Partner in the Eye
Though it can be uncomfortable at first, maintain a soft, open gaze before you enter the poses (and throughout in the ones that allow for it) to center you both and build trust.
Agree on a Signal
Squeeze once for "stop" and twice for "give me a little bit more," so that you can gauge through touch alone how far to take each pose.
Respect Your Partner's Comfort Level
Be aware of your partner's limits and your own. When either of you has reached the furthest point of flexibility, ease off.