Summarize the following:
Remove all fridges from the lot, and delete the phones so that the Sim can't call to get takeout. They'll complain about being hungry, but since they can't get food without a fridge, they'll die of starvation. Children and younger Sims can't die from starvation; the Social Worker will come and get them if their Hunger bar drops too low. If there are tombstones or urns of other Sims on the lot, it's possible for the ghosts to frighten your Sims. When a ghost frightens a Sim, the living Sim's motives will drop; if their motives drop too low, they will die of fright. Generally, the angrier a ghost is, the more likely they are to try and scare a Sim. Certain types of death result in angrier ghosts (such as a Sim killed by fire), and occurrences such as a kicked tombstone, selling the bed they slept in, or their partner marrying someone else will agitate ghosts. Elder Sims will eventually pass away on their own accord, though you can't control when it happens without using cheats. Once you have an Elder Sim, just continue playing them as normal; eventually, when their time is up, the Grim Reaper will come to collect them. If a Sim dies of old age, other Sims cannot plead for the Sim's life. Sims who Grew Up Badly when aging from Adult to Elder will die sooner.
Let your Sim starve. Scare your Sim to death. Allow your Sim to die of old age.