Gently, but firmly, without getting upset or judging yourself for straying, simply return to the simple physical sensation of the breath. Then do it again the next time, and again, and again, and again.
Somewhere in this process, you will come face to face with the sudden and shocking realization that you are completely crazy. Your mind is a shrieking, gibbering madhouse on wheels barreling pell-mell down the hill, utterly out of control and hopeless. No problem. You are not crazier than you were yesterday. It has always been this way, and you just never noticed. [...] So don’t let this realization unsettle you. It is a milestone actually, a sign of real progress. The very fact that you have looked at the problem straight in the eye means that you are on your way up and out of it.
In the wordless observation of the breath, there are two states to be avoided: thinking and sinking. The thinking mind manifests most clearly as the monkey mind phenomenon we have just been discussing. The sinking mind is almost the reverse. As a general term, sinking mind denotes any dimming of awareness. at its best it is sort of a mental vacuum in which there is no thought, no observation of the breath, no awareness of anything. It is a gap, a formless mental gray area rather like a dreamless sleep. Sinking mind is a void. Avoid it.
When you find you have fallen into the state of sinking mind, just note the fact and return your attention to the sensation of breathing. Observe the tactile sensation of the in-breath. Feel the touch sensation of the out-breath. Breathe in, breathe out and watch what happens.
Don’t set goals for yourself that are too high to reach. Be gentle with yourself. You are trying to follow your own breathing continuously and without a break. That sounds easy enough, so you will have a tendency at the outset to push yourself to be scrupulous and exacting. This is unrealistic. Take time in small units instead. At the beginning of an inhalation, make the resolve to follow the breath just for the period of that one inhalation. Even this is not so easy, but at least it can be done. Then, at the start of the exhalation, resolve to follow the breath just for that one exhalation, all the way through. You will still fail repeatedly, but keep at it.
Every time you stumble, start over. Take it one breath at a time. [...]
This meditation is a process of retraining the mind. The state you are aiming for is one in which you are totally aware of everything that is happening in your own perceptual universe, exactly the way it happens, exactly when it is happening; total, unbroken awareness in present time. This is an incredibly high goal, and not to be reached all at once. It takes practice, so we start small.
Excerpted from this article by Bhante Gunaratna.