When we practice insight (vipassana), we need two important mental factors -- mindfulness and wisdom.
Mindfulness covers two things, recognizing and accepting: Recognize anger as anger, pain as pain, and so on. When anger is present, know that anger is present. When greed is present, know that greed is present. Accepting means accepting what is just as it is, neither clinging to it nor pushing it away. This is mindfulness.
The non-self nature of things is to be understood by way of Dependent Origination. To understand non-self, we must understand cause and effect. For example, with the arising of eye-contact, feeling born of eye-contact arises. Contact is the cause; feeling is the effect.
We can apply this understanding directly in order to be released from the chain of suffering. This is a moment-to-moment practice until we reach liberation.
Whether observing a sensation, feeling, mind, or mental object, it is possible to practice using this same process as outlined here:
R RECOGNIZE IT. Recognize phenomena (anger, greed, pain, heat, joy, sleepiness, remorse, depression, fear, happiness...). This is mindfulness (sati) so that the mind does not go off on tangents.
A ACCEPT IT. Accept what is just as it is. Do not try to resist it, which causes the underlying tendency of anger in the mind. Do not try to cling to it, which causes the underlying tendency of greed in the mind. And do not add stories to it, which causes fantasies and restlessness. Accept it just as it is.
D DIS-IDENTIFY FROM IT. Do not identify the phenomenon as I, mine, or myself. It is simply a physical or mental state performing its function. Look upon it the way a third party would witness or observe another’s sensation.
I INVESTIGATE IT. Sometimes it is appropriate to investigate the cause of it. Where does this phenomenon come from? It is just the effect of causes, not I, mine, or myself.
C CONTEMPLATE IMPERMANENCE (anicca). Note the sensation as impermanent, changing, and passing away. Note it constantly and continuously. When one sees its impermanence, its unsatisfactory and impersonal nature also will become clear.
A ALLOW IT TO BE. Remember, whatever arises simply arises based on causes and conditions. Because those causes and conditions are themselves impermanent, the phenomena is as well. There is no need to be bothered or to try to change it; it will change by itself as we watch.
L LET IT GO. Do not cling to anything whatsoever. Whatever the phenomena, let it come and go, as if watching clouds passing in the sky. Contemplating impermanence teaches the subconscious to let go in due course.
But how is it possible to remember all of these steps? Just remember the acronym R.A.D.I.C.A.L.