Basically it is down to mechanics and yet goes beyond that. The manner in which the sexual organs are stimulated counts, but the psychological factors cannot be overlooked. What may please one may not please another. What may please one once may not necessarily work a second time. It's all about learning how we respond and react. The key is a varied practice, responding to your partners mood of the moment. You have to become sensitive to your partners body language and allow them to guide you. They may want slow and soft or slow and hard or hard and fast, etc. You've got to learn to feel what they want coz if you ask it takes the edge of their pleasure.

Does size matter, not unless you're below 4 inch. The vagina is generally around 5 inch deep, but most women don't enjoy getting it rammed into the cervix as this can be painful. Most of the nerves are at the mouth of the vagina and the g-spot is 2 or 3 inches inside. Also the majority of women don't seem to orgasm from penetration alone, they do need clitoral stimulation.

If you want to be a red hot lover, think in terms of her needs more than your own.

lol... just guessing...