First, I would kidnap a well-known, important political figure. Second, I would contact the League of Shadows Nations and tell them I want 500 Trillion dollars or I will kill the aforementioned political figure and release my army of highly trained clone soldiers upon the world. After they decline, I will not kill the hostage, but instead contain him a mile underground in my highly-refined dungeon, filled with booby traps and puzzles so that no one will get to him. Then I will sit patiently in my chamber, while all my minions wreak havoc upon the Earth. There I will wait until, inevitably, one lone person with no military training whatsoever manages to destroy all of my forces and makes it up to me. After a few words, I will trap him in a cage just before he has a chance to strike. Instead of killing him, I will then monologue about how trivial he is and how my plan will still succeed despite his efforts and order my minions to take him down to the dungeon with the other prisoner. I will return to my chamber and do nothing some more. The two prisoners will eventually escape and, teaming up, manage to make it out of my puzzle-filled dungeon with nigh but a scratch. The "heroes" will then again return to my chamber, catching me unaware and unprepared for an attack. This will enrage me to the point where I reveal my true form, destroying half my castle in my wake. There will then be an epic battle between the three of us. I will be far more powerful than both of them combined, but a fatal flaw in my fortress design will eventually lead to my downfall. Perhaps a chandelier or a trap door I forgot about. I don't really know yet. Deafeated, I will swear to return one day, and tell them they will rue the they ruined my plans. Triumphant, the heroes will return home and receive cake and many, many women.
And that's how I would take over the world.
...Wait, shit.