First of all, you have to ask yourself why you want to dominate the world anyway. You probably have some unresolved issues with your pet hamster. The world is a big and complicated place, and ruling it with an iron fist is alot of work. I'd rather rule a tropical island. That would be just the right size to rule. I would tell all the fish and coconuts what to do, and that would mostly be 'get eaten by me' and sometimes 'put on amusing puppet shows'.

If you really want to rule the world, here you go:

1. First off, you're gonna need some lasers. Go get some.
2. You're gonna have to assemble a crack team of loveable misfits, including a safe cracker, a smooth talker, a demolitions expert, a kung fu expert, a guy with too many opinons about pop culture, a Cheese Man, and another demolitions expert, but with a big scar on his face.
3. You're going to need to draft a very convincing letter explaining why YOU are the perfect person to be in charge of 7 billion humans, 70 billion other animals, a bunch of water and mountains, and the rest of the planet also.
4. You're going to then mail that letter to every president, prime minister, king, and warlord you have in your address book.
5. You're going to wait by the phone for them to call you, and whenenever somebody else calls, you're going to tell them 'get off the line grandma'
6. You're going to have a nutricious breakfast of fish and coconuts.
7. You should now check your email, take out the trash, do your taxes, and any other chores you've left untill the last minute.
8. You're going to design your King of the World costume. It should include lots of imperial majesty, and also a cool hat.
9. You're going to pick your nose. I just know it. Use a tissue like a decent human being.
10. You're going to take your laser guns, your crack team of loveable misfits, and a poodle named Snipzy and just start attacking the nearest metropolis.
11. Hack the Mainframe.
12. Crush all resistance to you with a surprizing gift for tactics and strategy.
13. Repeat steps 1 through 12 for all major continents and don't forget the oceans.
14. Sign a peace treaty, and then rip it into shreds, and feed the shreds to Snipzy.
15. Laugh Maniacally.
16. Cough Manically.
17. Have lunch.
18. Make sure everybody is doing what you told them to do.
19-34 Rule the world with an iron fist, or a fist of the metal of your choosing. Make sure people salute you, and that people who disagree with you are punished. At this point, you might want to enact lasting social reforms, for the benefit of all mankind and also dolphins, but most likely, you'll become increasingly paranoid, and basically turn into a big weirdo.
35. Create large statues of a slightly handsomer version of yourself.
36. Pool Party!
37. Die or retire or travel back in time or something. It's hard to think of a good ending to these sort of things that isn't anticlimactic. Maybe just hide on a tropical island somewhere. They're really nice.