Instructions
Play with a Sim until it dies naturally of old age. Open the Sim's status menu to see how far along its age has progressed. If it is already an elder Sim and the age progression bar is full, it may be taken by the Grim Reaper at any time. You can also adjust how fast your Sims age from the options menu if you want to speed this process along.
Kill one of your Sims or a computer-controlled Sim visiting your lot. Build walls around a pool while Sims are swimming to drown them, or put a Sim in a room without food and take away the door to let it starve. Fires are caused by Sims with low cooking skills using a stove, or from having too many objects near a fireplace. A Sim can also be electrocuted if it stands in a puddle while fixing an electrical object.
Place the remains left over from the Sim who died somewhere on your lot. If placed indoors, the remains become an urn. If placed outside, the remains are a tombstone. It does not matter where you place it, as long as it is on your lot. Alternatively, you can take the remains to another lot if you want the ghost to haunt that location.