In its colloquial usage, being mindful typically refers to being generally cognizant of what’s going on, usually what’s going on outside or around you. But its usage has more of a specialized connotation among Buddhists, and has specific reference to being cognizant of your mental states, whether these are produced through sensations in the body, or emotions or thoughts arising within the mind. .
I consider myself a “sola Vipassana” Buddhist. Instead of the Christian Protestant axiom of salvation from the guilt of sin and its damning consequences, by faith alone through grace alone, I advocate deliverance from the cycle of suffering that is samsara, by Vipassana (insight) alone through Anapanasati (mindfulness of breathing in and out) alone.
This doesn’t mean I condemn other spiritual traditions or other forms of meditation, of course. There are plenty of meditative practices and other spiritual practices within the Buddhist tradition, sometimes within the same tradition (samadhi and anapansati in Theravada), and plenty of interesting practices outside of Buddhism. I am convinced that this practice in itself, however, is sufficient for the cessation of suffering.
In order to practice it, focus on the sensations surrounding breathing by centering on either your abdomen or nostrils. I focus on nostrils myself, and empty my mind of everything except for the sensation of breath entering and leaving my nostrils. Periodically, you will experience the rise of various bodily sensations and mental and emotional impulses or volitions. When this happens, simply silently identify what you are experiencing in your mind, without assigning either positive or negative valuation to the impulse.
Neither repress nor condemn nor praise anything you experience. Simply give it its name and it will dissipate after a few moments. Suppose your nose itches. Mentally center on it and think to yourself “itching. Itching…”. Neither scratch the itch (literal or figurative) nor condemn it. Simply let your itch have its day in court. This principle applies with undiminished force to other itches as well, both physical and mental.
Suppose a thought arises, attached to a certain emotion, causing you to envy someone else because you wish you had their body or access to certain kinds of enjoyment. You are to think to yourself “envy. Envy…” in each case you will witness your attachment gently dissipate without much fanfare within a few seconds. Try this next time you are overcome with anxiety concerning an approaching bill or car repair or anything else as well.
This applies to positive affects as well. You may find yourself becoming elated during meditation. This is not a “bad” thing. But becoming attached to positive emotions is no less a source of suffering than bondage to negative ones. If you experience a sense of intense tranquility, make that the object of your mindfulness as well. It will also dissipate and you will incrementally approach a state of non-attachment to any affects whatsoever, a state in which suffering has vanished and peace reigns.