Positions are a key element in tantric sex, as these are important to master in order to achieve the best results. You don't have to focus just on them, but to go into a special mood where you gaze into her eyes and synchronize your breaths. Everyone has a favorite position and you can always alternate the following positions with your favorite; just try not to hurry things up, keep synchronizing your breaths and be passionate.
Battering ram
Although the name may suggest powerful thrusts, keep in mind to pace yourself and go soft. The woman lays face down, legs spread until the man penetrates. She then closes up the distance between her legs, crossing her ankles, this way creating a tight space that they both can benefit of. The man has partial control - he leans over her, using his hands as support, while the woman can lift her waist from time to time to enhance the sensations and even play with her clitoris while her waist is lifted.
Battering ram face up
She lays on her back with a pillow under her head, legs open, in the air. The man leans over and after he penetrates, she crosses her legs and puts them both on one of his shoulders. The man can softly rub her breasts and play with her feet, moving them from one shoulder onto the other, push them slowly away from him, spread them, then cross them back, kiss them, softly bite them. Feel free to do whatever you feel like as long as you pace yourself.
Modified missionary
This will become one of her favorites: she lies on her back, with no pillow under her head, but with a pillow under her waist so that her vagina is the most accessible. The man leans over and penetrates while using his hands as support, placing them somewhere in her bust area. Be careful not to go further, touching her breasts and leaving your whole body weight on her breasts - complete turn off and painful for her. The man moves in such way (downwards - upwards) that he stimulates the clitoris as well. From time to time take the matter into your hands and stimulate her clitoris with your hands or, better yet, take her hands and massage her clitoris with her hands.
From behind
...or doggy style, but not quite them same and more intimate than that. They both stand, but the woman leans forward and spreads her legs. She can use a chair or a desk to maintain balance and she can arch her waist in such way that the butt sticks out. She can also stimulate her clitoris with one hand as he can grab her waist or move his hands up and down her spine. Play with her hair, but be careful not to pull hard, rub her breasts and her ass.