Alright, of my afore mentioned categories, I have yet to do a world domination plot.
Being a king, president, or other title for a supreme potentate means you are the target for media, enemies of your country, enemies within your country, and may be limited by the law itself. However, if you are the one controlling the potentates, then you never take the heat. Put your own people in place (think Illuminati). Make loads of cash off of arranged wars. Oh, and don't let your loyal servants know who else is working for you.
How do you do this you ask? It can be quite simple. Blackmail is an easy way, but that only works for some and only for a little while. Greed is always the best way. Offer them more power like a Senate seat or rank promotion in the military. Don't tell them how you're going to do it, just do it. Maybe you have to kill someone or have them killed. Maybe you have one of your other cronies promote them for no reason at all. The higher up you move your pawns, the more secret information you receive and the more you learn about who needs to be eliminated and who needs to be recruited. Of course some will not be greedy for themselves, but for their country (which is even better). They may want to bypass the law, country policies, or red tape and get the job done. Once they begin making compromises, you'll have them hooked. If they start feeling guilty or are discovered you can either kill them off or make them take the rap for it.
The money will pour in and flow down to your subordinates. You control the world and no one knows who you are, so they can't eliminate you. They can't attack your country because you'll always have your other ones to either come to the rescue or profit from it. Kick back on one of your private islands with naked women serving you whatever drink you want or in one of your castles with lovely French maids (the ones that shave).