The following is Thay's method of contemplating emptiness.
(Emptiness)Sit in the full or half lotus. Begin to regulate your breath. Contemplate the nature of emptiness in the assembly of the five aggregates: bodily form, feeling, perception, mind functionings,
and consciousness. Pass from considering one aggregate to another. See that all transform, are impermanent and without self. The assembly of the five aggregates is like the assembly of all phenomena: all obey the law of interdependence. Their coming together and disbanding from one another resembles the gathering and vanishing of clouds around the peaks of mountains. Neither cling to nor reject the five aggregates. Know that like and dislike are phenomena which belong to the assemblage of the five aggregates. See clearly that the five aggregates are without self and are empty, but that they are also wondrous, wondrous as is each phenomenon in the universe, wondrous as the life which is present everywhere. Try to see that the five aggregates do not really undergo creation and destruction for they themselves are ultimate reality. Try to see by this contemplation that impermanence is a concept, nonself is a concept, emptiness is a concept, so that you will not become imprisoned in the concepts of impermanence, non-self, and emptiness. You will see that emptiness is also empty, and that the ultimate reality of emptiness is no different from the ultimate reality of the five aggregates. (The amount of time will be according to the individual-perhaps one hour, perhaps two.)
(Excerpted from Thich Nhat Hanh’s “The Miracle of Mindfulness”)
I understand that there are two kinds of the ultimate truth, one in the phenomenal world and one in the noumenal world. The former is emptiness (non-duality) as interdependent co-arising (two sides of the same coin). The latter is emptiness (non-duality) as wholeness (extinction of all notions). And the above Thay's contemplating emptiness is based on the phenomenal world. Emptiness is a notion, so we have to be careful not to be caught in it. Upon understanding the true nature of emptiness, we need to throw it away.
Thích Nhất Hạnh