Why do we tense our necks (II)?

One of the reasons, is simply because we don't care.
We are a lot more interested in doing what we are doing, like getting out of a chair for example, than in the consequences to our own health.

Altogether, one after the other

You start with freeing of the neck, which brings about the rest, "one after the other".
But you must think of it as "one thing": it will come out wrong if you think of doing it "one after the other".
If this sounds contradictory, consider for example that when you walk, you step your legs "one after the other", while you think of it "altogether" as walking.

Use your brain

This is the title of Noam Renen's aphorisms on the Alexander Technique. ( You may find them at http://members.fortunecity.com/noamrenen )
In my experience most teachers, including Alexander Technique teachers, are not ready to accept or even tolerate that his/her students explore by themselves, i.e. use their own brains!