The practice is simple. Focus as narrowly and as minutely as you can on a particular sensation (I will explain in terms of physical sensations, but this technique could be applied to the other senses too). I like to choose a pinprick point at the tip of my nose. Once you have zoomed in on this point as much as you can, to the point where you feel you have really isolated the ‘feeling’ quality of it and it is as small as you can possibly define that area, then in swift fashion, retreat your attention outwards to cover your entire body. From here, you try to spread your attention to include all bodily sensations simultaneous. Because of the nature of attention, the degree to which you know all these sensations is of a lesser quality compared to when you were homed in on just the one point of tactile pressure (e.g. the tip of the nose). Now, once you have the impression that you have had a sufficient conscious moment of full body awareness, turn it back around and dive into the fine-grained, sweet spot that you have already visited. Keep repeating this exercise of focusing on the smallest area you possibly can, and then subsequently the biggest area, and then the smallest and then the biggest and so on.
The benefit of this practice is you train multiple types of attention (both exclusive and inclusive attention). You are also practising your attention agility — the ability to quickly grasp something and then change gears in your mind rapidly. This makes you better at adapting to sudden context changes. The difference between an exclusive concentrated state versus an inclusive concentrated state is quite stark. Subjectively the mind feels pretty different and these attention suicides make you accustomed to both.
From having practised this I find that sometimes by the end of my sit it appears as if I start to encompass full body awareness and the detailed precision on a singular point at the same time. There is still some back and forth going on; but it is as if I can run the attention suicides faster, yet also in a way that I am able to keep one foot in the exclusive point (and maintain some of its higher microscopic power) while my main focus blossoms outward in the inclusive realm of attention.
A couple of body scans to become familiar with how your body is situated at the time.