As I said, through proper cultivation; i.e. conscious, dedicated expansion.

As an experiment, you may wish to attempt the following tonight (or perhaps something similar):

Sit in the lotus position, spine erect, tongue gently touching the roof of the mouth. After a few "cleansing" breathes, visualise white/gold light (most speak of white light but personally I see only gold) entering through your crown with each inhalation; and with each slow, deliberate exhalation, visualise this light entering your pineal gland and expanding further each time you exhale (as an orb, for instance). After some time, bring your awareness to the very heart of your third eye, and breathe slowly, relaxing as you are surrounded by white/gold. You may begin to see profound colour changes, perception changes (depth, intensity), and perhaps even experience mild discomfort behind and/or between your eyes - this is perfectly safe, however, and should give way to a most wonderful state of being within a short time. You may also observe an alarming mirage of images, some familiar and some utterly bewildering. (I have experienced some utterly horrendous and rather disturbing images before me - from where they came I do not know!)

On three separate occasions, while performing a similar meditation, I have been physically forced over by a rush of energy pushing against my forehead and chest. I have performed banishing (clearing) rituals ever since and have experienced no further interference...

And on a purely "physical" level, cleansing the entire body through fasting is clearly desirable.

Take care, and enjoy your Self!

In due course, one thing at a time.

essentially, humming the correct frequency, with the tongue pressed against the cutting surfaces of the top two front teeth, while exhaling, and making a "th" sound, beginning at high frequency and spanning to lower frequency, until you feel the pineal vibrating, then you know your frequency at which your mind's eye vibrates.
are you familiar with Royal Rife ?

It's just a guess.

That's a good idea.