Okay, my body acts like this:
Generally I lay down, but sometimes I stand up (like when I'm in the shower). Sometimes I do it while on my knees, when I'm recording a video on my web cam.
When I start, I generally have my eyes closed or I'm watching something. I generally start out using my fingers slowly moving them up and down the head of my dick.
I then being to move faster, using my entire hand up and down my entire shaft and head. This is where the facial expressions come into play. I generally have a faint smile on my face, as I enjoy what I am doing
By this time, the end is comming (lol). My face is gentally moving from a smile to the standard O face (raised eyebrows, mouth open, a look of almost pain, but actually of intense pleasure). My up and down hand movements are pretty rapid by now. When I orgasm, I usually moan faintly with an exhalation of breath and have a full body shudder.
Good question palm9000, I love it!