Exploit the following positions even if you will not engage into tantric sex because these are also the most satisfying positions declared by women. It's impossible not to have tried them (maybe the one in the tub), but if you have, you still might read something new and interesting from Tantra.
Woman on top
This position gives her complete control over the thrusts and the intensity of her sensations - the man lies on his back while she kneels down on his penis, her legs spread on both sides of his thighs. She can alternate and lower the angle from 90 degrees, leaning over the man.
The best way to take advantage of this position would be for her to move not only up and down, but back and forth as well. This way her clitoris gets stimulated however she feels like. In the mean time, the man should use his hands and not just lie there: grab her waist (but do not interfere with her motion), slowly slide your hands up and down her body, over the breasts, softly pinch her nipples, feel her lips, her hair, etc.
Bath tub
Similar to the one above, but her legs are forced inwards. The man lies on his back, leaned against the bath tub and helps her sit on his penis. She can move back and forth, rubbing her clitoris against his pubic bone, as he is gently massaging her breasts and keeps moving his hands all over her body, focusing on different parts of her body from time to time: her waist, her breasts, nipples, holding her hands as she is thrusting, etc.
On the edge of the bed
Here's how this one goes: the man sits on the edge of the bed and she sits in his lap, facing him using her tibia as support. Don't worry, this doesn't hurt unless you have rigid edges of the bed (you can also use a sofa, a chair, or an armchair). This is probably the most stimulating position for them, as the clitoris really gets stimulated and the penetration is deep.
Having your bodies so close also helps a lot more than in the other two cases stated above because besides playing with her breasts and stimulating her nipples, the man can suck on her ear lobes, kiss her neck, mouth, behind the elbow, etc.
It will probably sound weird, but try kissing and licking her armpit - it turns out to be as stimulating as the neck and ear lobes. Anyway, if you really love her or you know she's really clean, try it. It's worth the trouble.
