Breathing: The root of tantra is similar to that of yoga. Pranayama-the breath. Breathing circulated energy and helps tune you in to one another (as well as yourself). 
In Practice: On your own, breathe through sensations in your body. If utilizing self pleasure, breathe into the sensations and allow them to flow without your breathe becoming to rapid. And without holding your breath. 
With your partner, breathe together. You can sit facing one another or lay on top of one another and play with your breathe. Try exhaling when the other inhales and inhale when they exhale. Breathe Into One Another.