One should begin by reflecting on the qualities of nibbana, according to the Buddha's words:
“Bhikkhus, in so far as there are dhammas, whether formed or unformed,fading away is pronounced the best of them, that is to say, the disillusionment of vanity, the elimination of thirst, the abolition of reliance, the termination of the round, the destruction of craving, fading away, cessation, Nibbāna”
A II 34 (Nyanamoli, trans)
Practice most likely involves a mantra for each quality, for example, "madanimmadano" (disillusionment of vanity).
According to the Visuddhimagga, upasamaanussati doesn't lead to aapana samadhi, only upacara samadhi:
As he recollects peace in its special qualities of disillusionment of vanity,etc., in this way, then: “On that occasion his mind is not obsessed by greed or obsessed by hate or obsessed by delusion; his mind has rectitude on that occasion, being inspired by peace” (see VII.65, etc.). So when he has suppressed the hindrances in the way already described under the recollection of the Enlightened One, etc., the jhāna factors arise in a single moment. But owing to the profundity of the special qualities of peace, or owing to his being occupied in recollecting special qualities of various kinds, the jhāna is only access and does not reach absorption. And that jhāna itself is known as “recollection of peace” too because it arises by means of the special qualities of peace.
Vism VIII.249 (Nyanamoli, trans)