There are two things I want to cover regarding this question. The first is that it is best to not try to quiet the mind. That is fighting the mind and that battle will never end in victory for you no matter how long you fight. It becomes a never-ending battle. When you are trying to quiet the mind, you are actually agitating and fueling the mind to create more thoughts.
In the yoga sutras of Patanjali, on the first page, is the line, “Yoga is the cessation of the revolutions of the mind. Then the Seer [i.e. Self] abides in its own nature.” The mind revolves like a wheel spinning. So, when you try to quiet the mind, you are actually helping to spin the wheel and the mind continues to revolve.
Think of a hanging bicycle and you are spinning the wheel. How would you get the wheel stop spinning? Now you could just cease spinning the wheel and the wheel will slow and stop on its own. This is how the mind becomes quiet. You cease agitating the mind. You cease paying it attention. You cease fueling thought.
This brings me to the second thing…I don’t recommend witnessing your thoughts if you want to quiet the mind. You tend to get more of what you focus on. So if you are focused on thoughts, the mind just goes “oh, you want more thoughts to watch.” In this way, paying attention to the thoughts fuels the mind to create more thoughts. It would be better to cease paying attention to thoughts. Do not be troubled by thoughts. Let them come or not come and pay them no mind when they do come.
Now you could focus on the space between thoughts. In this way, the attention is on the gap between thoughts. Focusing on this space may lengthen the time between thoughts. Again, the mind gives you what you are focusing on. So if you focus on the space or gaps between thoughts, the gaps widen.
However, witnessing thoughts (or even the spaces between thoughts) could be a mental trap to fall into. You could mentally be watching the mental activity. How will this cease the revolutions of the mind? It would be better to get out of your head entirely.
Instead, inhabit the body and experience what the senses are giving you. This is not an action, per se, because we have no choice but to be aware of what our senses are giving us when we are conscious. But out of curiosity, see how much you can be aware of at this very moment.
Inhabiting the body is like an experiment in seeing how much you can be aware of within yourself…but this is combined with experiencing the senses and seeing how much you can be aware of everything around you as well. You won’t be able to be aware of everything (the conscious mind can not accept that much data), but out of curiosity how much can you be aware of in the now. This totally experiencing the now is what is called “being present.”
It is like we have a limit to attention or awareness. We only have so much to split between thoughts (which are only about past and future) and experience (which is only about now). When we focus entirely on experiencing the now and we become aware of more and more of what is now, thoughts slow down and become less and less. As the focus is on now, there is little room for thought because thought is only about past and future. It is also not relevant, so what thought does arise we don’t pay attention to it.
I have found that when I am totally present, I don’t have any thoughts what-so-ever. Several minutes and even hours pass without a thought. So I know it is possible to not think. Eckhart Tolle talks about having periods of time (sometimes hours) passing without a single thought. So I am not special in this experience, but it does require being totally present and not paying attention to thoughts even when they arise.
Don’t get stuck by thoughts…if you allow thoughts or the silence of no-thoughts to exist (either way)…it is easier for the thoughts to cease because we are not resisting them in any way.
Now don’t be present to try to quiet the mind. That is attacking thought again and it will not work, because you are still subtly spinning the wheel. Cease doing anything about the mind. Just sink deeper into the present…feel and experience more of what is here and now. Thought will slow on its own and may stop entirely. In this way, it is kind of indirectly quieting the mind. Even the desire to quiet the mind agitates the mind…let the mind be free and put the focus on the body and experiencing the now.
The mind resists, like a temperamental bull, any efforts to control it. You put fences around it, and it will kick at them and break them. You try to tie it down and it will do everything it can to snap the rope. Cease trying to control it, let it free in a wide open pasture with no limits. It calms down and ceases to throw fits and cause damage. It just stands passively in the meadow.
In the same way, trying to control or limit the mind/thoughts will only keep that wheel spinning. You have to let go of the wheel and cease doing anything with or about it. Thought may not stop immediately, but the spinning wheel will slow and cease of its own accord eventually.
If the mind does stop or you are aware of thoughts slowing, do not rejoice and try to hold onto that state. That is paying attention to the mind again. Again, this will agitate the mind and create more thoughts. Do not taunt the bull after it finely stands still. If thoughts stop and then they come back, pay them no mind…just focus on inhabiting the body and fully experiencing the now. Do not worry about quieting the mind…focus on feeling and experiencing the here and now fully. This will quiet the mind on its own.
In that silence and stillness of a quiet mind, you may realize the Self. For when the revolutions of the mind cease, then the Self abides in its own nature.