The first obsticle would be the government. you would need someone in there utterly devoted to your cause but not psychotic enough to get caught. once you had a man on the inside in a high if not the highest position to use as your puppet, then changes can begin.
The man in 'charge' for the public would be near perfect, not totally but nearly. everyone has faults after all so if they were too good then suspicion would arise to quickly to be snuffed. the reall mastermind however would always be in the shadows, never known, it would be safer that way.
give the populace the illusion of freedom, subltly introduce your own ideas of the world into thier systems through tv and school for the younger generation. for the older generation the working class that isnt being taught from a young age, mandatory health checks each month for work that include some sort of medication that has mind numbing agents in it that make the mind suceptible to ideas with the right pushes would be essential.
once you have your own country compleatly under control, then its time to build the military and prepare for war. along the way their will be casualites of course as those smart enough to see whats going on resist.
next is the other countries. same plan of course, with tweaks per each individual culture so it works the best to your advantage. once you have allies enough to take on the superpowers go for it and start a war that only you can possibly win, you must be patient enough to wait until your own allies and country is strong enough to withstand any hits from others and come out kicking.
once you have world domination, you look to the sky to see what or whom else you can conquor.
((and that is how I would take over the world. just a basic but you get the picture))