ST article "Coming to terms with death" by prof Chong Siow Ann is a good read. He advocates that it is better for people to be prepared instead of avoiding thoughts about death, so that they can leave the world in peace.
The article mentions a book "Talking about death won't kill you" by Virginia Morris where the author lists out the various fears relating to death which include:
-fear of body being dissected in a post mortem
-fear of being shunned and abandoned
-afraid there is no afterlife and only "unimaginable nothingness"
-fear of not gaining entry to paradise
In addition there is the accompanying worry of loss of dignity and autonomy when dependent on others to meet basic hygiene and physical needs. There is also the fear of being a burden to family members as well as not having settled some unfinished business.
The author thinks that those who live with the awareness of death and staying engaged in life for whatever time that remains have better outcome in the face of dying. In that respect the " 5 key tasks" that need to be carried out would be to say " I'm sorry, I forgive you, Thank you, I love you, Goodbye".
Personally I agree the most fearful is this "unimaginable nothingness". It's like some obliteration, some snap elimination from this world that has so much history. It's like I will never know forever how it will evolve. Hence the fifth task saying Goodbye is the hardest. This is often termed as existential death anxiety and is what make people turn to religion.
A teacher once said that to be calm and peaceful at death, one should imagine either following a divine being or imagine immersing into the vastness of the universe.
The ST article ends with a quote from neurologist cum writer Oliver Sacks before his death "I have loved and been loved, I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal on this beautiful planet, and this in itself has been an enormous gratitude and adventure".