The concept of sunnata, voidness or emptiness, is one that is central to an understanding of Buddhist thought. It is also very elusive and difficult for beginners to grasp. In fact, it cannot really be understood by the intellect alone, but must be approached by way of direct experience. As one matures in insight practise, the essential emptiness of all dhammas become more and more evident.
There is also a series of contemplations in the Cula-Suññata Sutta (Shorter Discourse on Emptiness, Majjhima 121) that deserve to be better known. In this Sutta, the Buddha lays out a graded series of meditations which allow the mind to approach a direct experience of voidness.
Below, I've given instructions for a way to do this meditation. Two general points should be borne in mind -
1 - Each stage is arrived at by a process of selective non-attention to some aspect of the total field of awareness. This may seem strange to those raised in the insight tradition, but this is how it works. Remember, with each successive stage, you are adding nothing new. You are simply removing attention from some aspect of the previous contemplation. There is nothing to attain, and nowhere to go.
2 - Don't try and "figure it out." The analytical mind is not of much use here, and attempts to engage it will only obstruct the process. This is especially so in the later stages; the best way to understand each stage is that it is what is left when you remove the previous object of attention.
The meditation proceeds through the following seven stages. As a rough guide, you should spend five to ten minutes in each one, but don't be dependent on a clock, just let it unfold naturally.
I - Begin with contemplation of village - this is a simple mindfulness exercise. Be aware of your surroundings, as they actually are, the room, the furnishings, any other people. Don't analyze or judge or compare. Just hold the surroundings in mindful awareness. When this is established, extend your imagination beyond the visible surroundings to take in the immediate area, the street etc., extending only as wide as is comfortable for you. ("village" is used in the Pali as a word for the quotidian human environment)
II - Next, move on to contemplation of forest. Simply remove all human constructions from the previous mind-field and focus only on the natural world, the plants and trees especially. Remember, selective non-attention. You don't add anything, you subtract. The "forest" was a part of the first contemplation, now you make it the foreground by non-attention to "village." Allow the field of your imaginative awareness to extend to take in the locality where you live, beyond your range of vision. If you live in a city, there are still lawns and parks to focus on.("forest" is used in the Pali as a word for the natural environment)
III - Next, by selective non-attention to the living world you move on to contemplation of earth. By non-attention to the living growth, become aware of the wide earth-element underlying things. Be aware in the imagination of the hills and valleys, bowls for any nearby lakes, etc. Allow your field of imaginative awareness to gradually expand until you are holding the whole globe of this planet in awareness. Focus on the solidity of the earth-element.
IV - Next, by non-attention to earth one should become aware of boundless space. At first, this will be the space occupied by the earth. Removing the earth from awareness, space becomes the foreground. (Again note it was present all along - we subtract and do not add) Space by it's nature has no boundaries, so the idea of an earth-sized area should quickly dissolve into boundlessness. Hold the awareness of boundless space.
V - Your consciousness is now filling boundless space. Okay, stop noticing space and only pay attention to the boundless consciousness. Mind without limit.
VI - In the next contemplation, we stop paying attention to boundless mind and let your awareness rest on the nothingness that remains.
VII If you're able to take it this far, eventually even nothingness starts to seem "busy". In the next step we remove the concept of nothingness from our field of awareness and rest in the field called "neither-perception-nor-nonperception."
It is not perception, because there is no perceiver and no perceived, but it is also not non-perception because it is not a blank annihilation. But don't try to figure it out. The name is not important, it's essentially meaningless, it's best to simply think of it as what's left when you remove nothingness.
After holding this for a while, return to the body with some mindful breathing before getting up. Good luck with this if you are inspired to try it.