My evil plan to conquere the world was:
1) Start as a troop soldier in an army:
- get some experience,
- get decent equipement
- build relationship with lords
- get a little money
- invest money in land and/or enterprise (good suggestion for the enterprise, I originally had not though about it)
2) Make more money, build a highly skilled small group of fighters, get some renown:
- recrute companions and a few troops
- kill small groups of bandit to get troops some experience
- invest into lands, trade, ships (haven't tried yet): need to get a large revenue base before starting to get a large army
- participate into tournaments: get money, items and renown
- do quests to get money, experience and renown
3) Get vassal and get some castle cities
- find a king that want you and you have good relation with his lords
- improve relation with the king and lords
- conquere castle and cities close to each others and improve them
- build a powerfull army
- get more money (you never have enough

)
4) kill everybody:
- betray your king when he refuse to give you a nice additional city
- recrute some lords
- kill everyone else

- conquere everything