How high the head should be for cutting
The first thing was that the sections being cut were vertical section which initially started in the area of the front hair line at the temple. The hair was being pulled out at ninety degrees or straight out from the head. The point of interest for me was that it was pulled to her body slightly below her shoulder level. I would estimate it was an inch or two below the height of the shoulder. This was higher than my usual height for cutting so I adjusted this in trying to copy her cut.
When the stylist was cutting across the top of the head the hair was being pulled straight up for cutting. These sections were cut at a level some where between the level of her chin and her lips. I made this adjustment also.
Keeping back straight and body at a slight angle
The next was that the stylist remained with her spinal column erect. In my previous attempts to copy these demonstrations I found I was frequently leaning to my left by bending at the waist. This was to aid me in seeing the guide. This stylist stood slightly behind the section to be cut with her left shoulder closer to the head and her body on a slight slant to the head. She would comb the section she was going to cut and comb the uncut hair away so she could see the cut line or guide from the previous section. The uncut hair was to her right so she would peek around the section so she could see the cut line from the previous cutting.
Keep fingers vertical and check where hair falls when cut
The fingers of the stylist were vertical to the floor. What I had been doing was allowing the tips of my fingers to tilt to the front of the head and the bottom of my hand to go toward the back of the head. In effect I was cutting with a diagonal back angle within the section. I used the example to help me to keep my fingers vertical to the floor while cutting. Watching her cut in this situation you could see the cut pieces of hair fall to her open palm. When I copied this position the hair pieces fell on my palm and wrist. If it was not falling there I knew my fingers were no longer vertical to the floor.
Keeping the fingers vertical also lets you check that the hair is pulled straight out and is neither over directed nor elevated all of which is covered in the commentary. Checking this was helpful.
How long is each cut of hair
The stylist would cut with long cuts of up to 2 inches in a palm to palm manner when this length was available. I have not mastered this and frequently cut in smaller cuts.
As a follow up on finding the guide, I recalled that Don Haidl at a course at Sassoon in Chicago had told me to take 1/4 of new hair and 3/4 of cut hair in forming a new section. Prior to this I had seen people recommend taking 1/2 and 1/2 measures. Taking the smaller section of uncut hair made it easier to see through to the guide. I could not tell exactly how wide the sections were in the demonstration , but when you watched the cutting they all seemed thin. She continued to look for the cut line or guide by combing the uncut hair away until she could see the cut line.
Use ear lobes to determine back hairline
One other thing was the position of the back hair line. With the head upright, this hair line seems to be at the level of the bottom of the ear lobes or within an inch of this line. This may turn out to be a useful reference to tell where to start the tapers in the back.
Use extra light to see guide
In practicing this cut on a mannequin, I brought a floor lamp close to the head to be sure the cutting area was getting a lot of light.
I saw some improvement in the general shape and in the uniformity of my cut. I expect that paying attention to these points of cutting will help me to be more consistent in cutting.