We should keep death always in mind.
http://measurelessmind.ca/maranasanna.html

The recollection of death is explained in AN 6.20
Dutiyamaraṇassati Sutta:
Here, monks, as day departs and night sets in, a monk reflects:
‘The [possible] causes of my death are many. A snake, scorpion, or
centipede may bite me. My death could occur because of that. That
would be an obstacle for me. I may stumble and fall down; the food
I have eaten may trouble me; my bile may be disturbed; my phlegm
may be disturbed; my [internal] winds may be disturbed. My death
could occur because of that. That would be an obstacle for
me.’
Then, monks, a monk should reflect: ‘Are there any worthless,
unskillful qualities that I have not given up that would be an
obstacle for me if I were to die tonight?’
If, monks, upon reflecting in this way, the monk knows that ‘There
are worthless, unskillful qualities that I have not given up that
would be an obstacle for me if I were to die tonight,’ then he
should engender extra desire, effort, diligence, energy, zeal,
mindfulness, and full awareness for the abandoning of those very
same worthless, unskillful qualities.
Just as, monks, if someone’s turban or head was burning, they would
engender extra desire, effort, diligence, energy, zeal,
mindfulness, and full awareness to extinguish the fire; in the same
way, the monk should engender extra desire, effort, diligence,
energy, zeal, mindfulness, and full awareness for the abandoning of
those very same worthless, unskillful qualities.
But if, monks, upon reflecting in this way, the monk knows that
‘There are no worthless, unskillful qualities that I have not given
up which would be an obstacle for me if I were to die in the
night,’ then he should abide in joy and gladness, training day and
night in skillful qualities.
The benefits of the recognition of death are described in AN
7.49 Dutiyasaññā Sutta:
‘The recognition of death, monks, when developed and cultivated,
is of great fruit and benefit; it merges with the death-free, has
the death-free as its end.’ Thus it was said. In reference to what
was it said?
Monks, when a monk’s mind frequently remains acquainted with the
recognition of death, his mind shrinks away from, recoils, pulls
back, and is not drawn toward longing for life, and either
equanimity or dislike are established. Monks, just as a cock’s
feather or a piece of tendon, when thrown into a fire, shrinks
away, recoils, pulls back, and is not drawn in; in the same way,
when a monk’s mind frequently remains acquainted with the
recognition of death, his mind shrinks away from, recoils, pulls
back, and is not drawn toward longing for life, and either
equanimity or dislike are established.
If, monks, when a monk’s mind frequently remains acquainted with
the recognition of death, his mind inclines toward longing for
life, or if admiration continues, then he should know, ‘I have not
developed the recognition of death, there is no stepwise
distinction in me, I have not obtained the strength of
development.’ In that way he is fully aware there. But if, monks,
when a monk’s mind frequently remains acquainted with the
recognition of death, his mind shrinks away from, recoils, pulls
back, and is not drawn toward longing for life, and either
equanimity or dislike are established, then he should know, ‘I have
developed the recognition of death, there is stepwise distinction
in me, I have obtained the strength of development.’ In that way he
is fully aware there.
‘The recognition of death, monks, when developed and cultivated, is
of great fruit and benefit; it merges with the death-free, has the
death-free as its end.’ Thus it was said. And in reference to this
it was said.
Sustained, dedicated practice of the recognition of death will
gradually create the optimal conditions for the arising of all
seven factors of awakening. SN 46.68 Maraṇa Sutta (abridged):
Here monks, a monk develops the awakening factor of mindfulness
accompanied by the recognition of death, dependent upon seclusion,
dispassion, and cessation, resulting in letting go. He develops the
awakening factor of dhamma-investigation accompanied by the
recognition of death, dependent upon seclusion, dispassion, and
cessation, resulting in letting go. He develops the awakening
factor of energy accompanied by the recognition of death, dependent
upon seclusion, dispassion, and cessation, resulting in letting go.
He develops the awakening factor of joy accompanied by the
recognition of death, dependent upon seclusion, dispassion, and
cessation, resulting in letting go. He develops the awakening
factor of tranquility accompanied by the recognition of death,
dependent upon seclusion, dispassion, and cessation, resulting in
letting go. He develops the awakening factor of meditative
composure accompanied by the recognition of death, dependent upon
seclusion, dispassion, and cessation, resulting in letting go. He
develops the awakening factor of equanimity accompanied by the
recognition of death, dependent upon seclusion, dispassion, and
cessation, resulting in letting go.
It is in this way that the recognition of death is developed and
cultivated so that it is of great fruit and benefit. It is in this
way that the recognition of death is developed and cultivated so
that one of two fruits is to be expected: either final gnosis in
this very life or, if there is a residue of clinging, the state of
nonreturning. It is in this way that the recognition of death is
developed and cultivated so that it leads to great good. It is in
this way that the recognition of death is developed and cultivated
so that it leads to great security from bondage. It is in this way
that the recognition of death is developed and cultivated so that
it leads to a great sense of urgency. It is in this way that the
recognition of death is developed and cultivated so that it leads
to dwelling in great comfort.