If you are tired or would prefer your man to do the bulk of the work during sex, then you should try some of these lying on your side positions.
Alternately, you can help by lifting her hips from behind to achieve an up and down motion.
You kneel between her legs so your mouth is at the same height as her clitoris.
Have her lean forward or back to change the angle of the penis for greater stimulation.
To lengthen lovemaking, start there then switch to a position that maintains clitoral pressure without so much pelvic back and forth.
These positions are more innovative, and perhaps not as widely known or practiced as the ones listed above.
Sit on the edge of the bed or on a chair with your feet on the floor.
You can add a variation to this by having her lean forward, so that her head is actually almost over top of your feet.
Honestly, I think that you should try out spooning or even good ole missionary.