(I am not sure this is a philosophical question, and this is not really a philosophical answer. But I think it is close enough.)
One answer from psychology is meditation of various kinds. From a certain Dialectical-Behaviorist perspective, we think we are immortal because we identify with the 'talking' mind, which rationalizes the frailty of the body away, as defense of its own territory. (When left entirely to its own, the 'talking mind' makes us all Platonists, convinced that it is itself going to survive beyond this world.)
If that is the case, then we come back into rational contemplation of our mortality, not when we are thinking about it consciously, but when we are fully immersed in physical sensation and not abstracted away. For instance, when we notice that the water does not feel exactly the same way it did when we were children, and we let that unconscious awareness sit with us. This takes place most directly when we purposely pursue and sit in Lacan's 'Real' or Winograd's 'thrownness' as versions of Heidegger's 'Dasein', moving away from purpose and intention viewing the related feeling of 'readyiness-to-hand' objectively and insisting upon dismissing it immediately. (Basically a demystified view of ordinary mediation as it appears almost everywhere. But not the kind that makes the experience of time 'fly'. The kind that makes it feel like time is very slow.)
For those for whom straightforward meditation by physical immersion is difficult, various cultures have proposed forced meditation, using a substance that pushes the conscious mind into the background, and pulls us forward into the sensory apparatus and the distortions of memory directly. Among those that often increase awareness of mortality are low doses of mescaline, which raises subconscious images of death and morose contemplations directly, and dimethyltriptamine, which creates otherworldly waking-dream style presentations of our experience and memories for the affected individual to learn how to navigate.
This theory is one of the reasons that those with terminal illness are sometimes introduced to psilocybin to reduce their fear of death. If they have not taken these other substances when they were younger, direct contact with reminders of death is not productive. But pulling their awareness into a more pure sensualism helps them psychologically even if due to their illnesses, the resulting sensations and experiences are not positive.
