This one we often do lying down. Sweeping attention through the body to sense its nature as a body, as the elements, then seeing the image of the skeleton, flesh dried up and blown away. This is a simplified version of the sequence of visualizations given in the classical sequence (and you can find a full version of Anālayo guiding the Death Contemplations (maraṇasati) here). Then resting with full-body awareness, and the breath, aware that each in-breath could be one’s last, and each out-breath a letting go.
Discussion on the implications and experience of the death contemplation.