Learning how to die is the domain of philosophy. But doing it gracefully is largely an engineering issue. There is largely only one chance to get it right so there's some value in learning the how.
Consider how awkward it is for another person to advise a dying man how to die with grace who is otherwise completely clueless about it. The time to learn this is when you are cognitively sound.
While I'm not at all qualified to talk about this, those who do are no longer around. So let's settle.
Genres of death
Death is either an event (sudden) or a process (prolonged). You should wish for a sudden death, not a prolonged one. This is setting aside the pain that loved ones will have to endure but in either case it amount to about the same.
What if a swift death robs you the chance to complete unfinished business? You should've thought about that earlier and take care of them before it's too late.
In the event of a sudden death, there's nothing much to explore. Circumstances are outside your control, there's no sense of grace to aim for. But not everybody is that lucky. Most of us don't have wars to fight, swift death is a priviledge.
It's when death makes a long and drawn out process that it becomes a problem.
When to call it
When the end is coming the worst thing to do is to overstay your welcome. Most doctors know this and choose to do nothing with their terminal disease. They have been around the block enough to know when to call it quit.
In the moment the only factor left is courage. Would you have earned enough courage-credit to declare you're done? Acquiring this courage is a big deal but is beyond the scope of this piece. Spiritual guidances are plentiful out there.
When courage is taken care of, the next thing is having to recognize when the end is near.
What if you're not given a terminal illness, how do you know when to call it? That's the hard part. Do you measure only bodily failure? What about the wetware, the cognition?
We can start with a simple scenario: when you can't control your bladder anymore. At which point we're talking about total reliance on another human for simple bodily function, where it's fairly certain there's no getting better from there on. This is a good point to mark the last chapter.
Going one step further, what if your body is running fine but the mind shuts down, be it from coma, dementia or any form of brain decay?
One of my worst fears is for me to regress slowly to a teenager state of mind. I'll be dumb like a brick, self conscious enough to realize it, yet have absolutely no ability to rectify it.
In the midst of it you can't be there to make the decision to declare you're giving up. This decision has to be pre-made and made known to dependents.
Example of an algorithm: if you show no sign of recovery from Alzheimer's disease in another six months, someone should find a way to put you out.
I'm a proponent of the dead man's switch. If I'm debilitated for over say three months, have no ability to stop the trigger, a message would be sent to the chosen person with clear instructions of how and when to put me out, along with my crypto-assets as inheritance.
Decision like these are easier with a sound mind than in distress.
Calling it a life
What does it mean to execute end-of-life after declaring it?
At the basic level it means putting a stop to painful attempts at recovery.
If life is suffering then death should attempt to be a delight. There's no point making the exit more painful than it has to be. This is the moment to indulge in every possible pleasure agent there is. I imagine drugs, alcohol, anything that rocks your boat.
Finally we end the show with euthanasia. Bring the party to where it's legal and make it a celebration.
Think of it as dessert after a lifetime of existence.
Conundrum of god's will
If you're religiously inclined, there's another level of complication where the will of god is involved. Taking active steps in ending one's life is strictly frowned upon.
Sure. In that case may I persuade you that continuous medical intervention is also violation of god's will, delaying the divine inevitability. Perhaps if you stop doing just that you'll still be staying on god's good side.
There are many details left unaddressed. How is euthanasia performed? What about edge cases like multi-year coma with a chance of resuscitation (like Steve Rogers)?
In domains where there are established expertise (euthanasia) I'll defer to them. Where there are none I'll leave it to your imagination.
I reserve the right the change my mind about any of these. Perhaps you can tell me how this framework could be invalidated. If I'm wrong, how would I know?
I'll end with a heuristic that I've never heard of but the irony make it feel true: those who control their death gets superior control over their lives.