first of all you need to find some available land, or get alot of weapons to take land from somewhere else.  then you would need to find a way to get subjects, or citizens.  then you would need to create an economy wether it be agriculture or industry.  and then you would need a parlement or congress to make sure that you dont go hitler or something.  thats about it, oh yeah and you need to collect taxes to fund your government and raise them incrementally to give yourself a raise every once and a while.