first I would seize control of a African country (allot of African countries have a unstable government so it wouldn't be to hard) I would spread a message of peace and try to unite the countries under one flag.
Assuming there are still ALLOT of diamonds/raw materials left in the ground I wouldn't need to worry about money I would simply buy allot of weapon,s/ military vehicles (tanks,jeeps etc.).
Since allot of people would like me (I created peace in their country) I wouldn't need to worry that much about a coup d'etat I could use the army to take over other countries (pretty much taking over any country standing in my way snowballing my resources/men at arms)
WORLD DOMINATION
(yes this is how I would take over the world)
-funny version-
mech jack this
???
WORLD DOMINATION!!!!!
-alternative serious plan-
get a monopoly on something (like MS has with Windows but bigger something you can,t copy)
and simply BUY the world.