Look up in their character profile where the soon to be dead is right now (usually "reining in x, y"), place your spy master there to build a spy network and almost every assassination will be about 40% success, 10% of getting caught, I even had 40-20 for the Kaiser, you get the boosted assassination stats the moment you move your spymaster there so it can all be done while paused.
Another part of this is getting good spymasters, what I like to do is go through the character search function for: Men, not married, not in prison, then arrange them by Intrigue and find some likely girl to matrilinealy marry him to, after the latest patch this can be somewhat difficult though, having a spare daughter lying around can be useful, and make sure the future spymaster has no claims or comes from a great house so he won't mind giving up his family name for the good of your's, ignore anyone who's not a courtier.
You can ofcourse also fix this with good breeding in your family, but I prefer to get spymasters from outside as they tend to die a lot if you let them spy for technology most of the time like me (finding some random arabian/north african county who are far away from you is generally best).
) my great-nephew inherit the throne. This is after three children, three brothers, and a few other heirs died (madvking induced and not). But my king is still kicking around at 71.
![[party]](/images/smilies/partytime.gif "Party [party]")
