1.Sitting virasana or siddhasana (my 2 favorite postures for any kind of formal session) in a silent place (relatively…not so easy to get nowadays) I get into in a state of global receptiveness to whatever sanna surfaces.
2. One should switch between environment and body sannas.
3. So let’s suppose that i start by noticing i.e. the distant noise of a car – I listen to it for some seconds (usually not more than 5) but don’t elaborate on it meaning why it pleases me or not pleases or neither.
4. Then i turn my attention/focus to the body and notice the nature of the contact between my pelvis/tighs and the floor, which may include sensations of temperature, softness or hardness,etc doesn’t matter in fact, i simply notice it for not more than 5 secondes and move on to an “external”/environmental sanna i.e. :light nuances let’s suppose…
5.then again back to the body i notice my breathing-rhythm without interfering with it. And so on.
There are also sannas related to energy between the skin and more or less 3 mm around it (can this be the gandhabba?) but whatever the sanna one shouldn’t stick (starting elaborate on it based upon memory or expectations) to any in particular.
This technique includes also citta-sanna : when something pops-up one should proceed same as above.
Practiced in Chan Buddhism. This is the Chan way of not getting entangled in and by vacisankhara.
At first sight it may look strenuous but in fact after 15 minutes one starts noticing i.e. that the body is much more relaxed than at the beginning of the session.
It can be also practiced extra formal sessions.