Mahasi Sayadaw began a revolution in insight practice in the mid 1900's in Burma with a technique called "noting" that is based on numerous texts, among them a sutta in the Middle Length Discourses of the Buddha called #111 One by One as They Occurred (Annupada Sutta), and #10 The Foundations of Mindfulness (Satipatthana Sutta).
His classic text "Practical Insight Meditation" is available many places and provides key instructions as well as a good basic map of insight territory.
It is a very simple technique in its instructions, and but its astounding power to produce direct insights should not be underestimated. It was and is the foundation technique of many of the members of the DhO, though most have used many other techniques as well.
The basic instructions are to make a quiet, simple mental note of all sensations that arise, concentrating generally on the breath when sitting and the feet when walking. On retreat, this is typically done with alternating hour sitting, hour walking, hour sitting, etc., for most of the day.
When noting breathing, for the in breath, one notes "rising", and for the out breath one notes "falling", and notes as many times as those are noticed. One might also note "in" and "out".
When walking, one notes the "lifting", "moving" and "placing" of each foot as it leaves the ground, moves through the air, and is placed on the ground again. Noting "turning" when one turns can help one avoid becoming lost in thought on the turns.
When distracting thoughts arise, one simply notes "thinking", when sights arise "seeing", when sounds arise "hearing", when the mind is wandering "wandering", when there is pain "pain", when there is joy "joy", when there is bliss "bliss", when there is restlessness "restlessness", when there is dullness "dullness", when there is sleepiness "sleepiness", when there is energy "energy", etc.
In this way, every sensation can be known as it is, every sensation can be noticed, every sensation that arises can be included in practice. Along those lines, one is advised to note every sensation that arises for the entire practice session, which is every waking moment when on retreat, such that even "eating" and "chewing" may be noted, "brushing" the teeth may be noted, etc. The exact word used is not so important, but that we are mindful and note with continuity and precision is.
As one progresses, one may note more rapidly and inclusively, noticing the sensations that make up the breath or the motions of the feet many times in one step or one breath, and thus begin to notice the true nature of those sensations and their Three Characteristics.
As one progresses further, one may begin to perceive things too rapidly to note them, such as in the insight stage of The Arising and Passing Away, at which point one may switch to generalized noting or drop the noting entirely and just be with bare vibrating or flickering sensations until such time as one needs the noting again to stay present and grounded in one's sensate reality.
Noting as a practice tends to give practitioners a very good appreciation for the value of the map known as The Stages of Insight.