Go for doggy style, get her knees at a distace a little bit larger than her shoulders distance and her ankles close or better crossed.
So:
Doggy
...Knees at a distance bigger than the distance bebetween her shoulders
......Ankles crossed
You can always touch her clitoris or she can enjoy her clitoris while you work on doggy..
If you are looking powerfull orgasms for her you can try your fingers on her pussy(such a wonderfull world waiting for you to discover it). Get her hot and go real slow with the moves and the pressure. In time you can build up intensity(rhythm, presure). If you are calm and you enjoy pling with her apply the same rules as when edging(she need to tell you when she is on te edge so you can slow down or stop

)
I would say that the landmark is the clitoris, but hear this:The land mark, checkpoint,
what you should pay attention is her HOLE BODY.
Discover it and get high!
This after the hot prelude..
About dick size, get more confident about yourself.
Enjoy