I have to agree with all the above. They seem right on from my experience.

As for streching the skin under the neck I find pulling the skin taut right above the collar bone and tilting my head slightly back pulls the area pretty taut.

As for were your running into situations were you need to pull the skin taut in an area that you have already lathered and not shaved yet I can only suggest experiment with were you start your shave to find what works best for you to stretch the skin with out that problemed.

Also spend some time in front of the mirror first using just facial movment to stretch your skin, then use your hand to stretch the skin around then a combination of the two you will be suprised how many different ways you will find to stretch different areas.