You should get yourself a copy of the book "Treat Your Own Neck" by Robin McKenzie. Its pretty cheap on Amazon. I believe this is the Robin McKenzie that "McKenzie chin tucks" comes from. It's a good book and will explain exactly how to chin tuck and also a whole bunch of other exercises to repair the neck and improve posture.

The way Dr. Mike explains it in his videos is that you bring the back of the head up and tuck the chin I believe. 

Horizontal dental plane is a good start, but experiment with lower and higher angles too until you find an angle that gives the largest postural benefits. Your preferred angle will change over time as your jaws move up, so it's useful to keep re-learning the chin tuck on a frequent basis.

Those are two different exercises that most people, including physiotherapist, confuse. They both attempt to treat the same problem but target different muscles. The one Dr. Mew is showing revolves around elongating the muscle versus the second one which is pushing back.

I think the exercise Dr. Mew is showing is the one that the majority of people with forward head posture would benefit from. Keep in mind if you have other postural disorders down the spine those need to be corrected to succeed in forward head correction.