I acknowledge this graphic from the Net.
In this 96th dharana and 122 Verse of Vigyana Bhairava Tantra, Shiva says:
Focusing on one excluding others
In that void still being perceived
Reach Shiva state
This dharana is probably the essence of all dharanas, which by definition are the focusing on one object with one sense. For instance, in trataka meditation, one focuses with the
sense of sight; one may instead use the hearing or feeling or smelling sense to meditate. Bt=y extension, this dharana also refers to all forms of mantra and image based meditations, in which
the meditator focuses on one mantra, say Om, or an image say of Shiva.
In all such efforts, our mind plays a game with us. Even as we try to focus, in fact the more we try to focus, more the mind slips away, letting other objects and thoughts to slip in. In short we lose focus.
Dozens of books have been written by experts on what focusing means. Shiva explains it in one verse. No need to pay several dollars and spend hours reading hundred of pages, the essence of which,
if the author knows anything about focus, would be what Shiva says.
Focus is the exclusion of everything else except what one focuses on. How simple and elegant? Everything else is a void.
I have read several books ranging from a 40 year classic by Gendlin to a more recent one by Leo Babauta, ranging from scientific to zen. Gendlin talks about stages of clearing the space, felt sense of the
problem, resonating handle, asking, and receiving. Leo talks about simplification, slowing down, small chunks, in the flow and other mindful processes. None of these experts are wrong, nor are they completely
focused on how to help others focus. You can do all these and yet wander unfocused.
Shiva’s state arises from creating void first of all other thoughts not by concentration but by gentle disengagement leading to replacement of other thoughts by the chosen one for focus. Even the thought one
focuses on is merely witnessed with no pressure to stay. Finally, even that thought or image or sound or movement can be witnessed by disengaging the mind. The dharana leads to dhyana leading to samadhi.
Focus leads to meditation leading to complete witnessing.
In the beginning it is critical to choose an object or thought to focus on that resonates with your default primary sensor. If you are visual, use sight; if auditory, sound. In the rest of Vigyana Bhairava Tantra
Shiva provides many techniques to suit each sense. The 112 techniques of Vigyana Bhairava Tantra cover all that needs to be known about focusing, meditation and witnessing. Every other technique taught
today as meditation by any culture or religion can be traced back to this source.