But first, let's pick a place to start. Beginning in 1066, I have three potential starting locations to decide from, all minor counts of little reknown.
Dublin (Ireland) - Normal
Pros
Independent - No liege to tax you or drag you into un-needed wars.
Tyrannical (chosen play style for this) - Easy to get land and money.
Big family - Hard to kill.
England - The nearest major power is embroiled in a succession crisis, leaving you with less to worry about.
Cons
Independent - No liege to protect you if someone declares war on you. Less scope for politics.
Tyrannical (chosen play style for this) - Everyone will hate you, quickly.
Big family - Lots of claimants.
England - Your big old neighbour is a massive threat as soon as those succession wars finish up.
Braganca (Iberia) - Harder
Pros
Vassal - Your liege will protect you when the moors attack. You can also use politics and intrigue to expand in the early stages.
Weak Liege - If you expand enough, Duke Nuno and even King Garcia can be toppled.
The Moors - Plenty of land to grab in holy wars and muslims to defend against for bonus prestige and piety.
No family - The only claimant to your throne is your liege Duke Nuno.
Cons
Vassal - Your liege will provoke the moors into attacking. Constantly.
Weak Liege - King Garcia is easily defeated by the moors and his vassals hate him enough that they will never bother raising levies to defend their own god-damned counties. Oh, and the moment he dies Castille will absorb everything into a nightmarish super-state with poor expansion opportunities for yourself.
The Moors - More numerous, richer, more powerful and vastly more technologically advanced neighbours who really, really want your land and will gang-rape you as a result of powerful alliance chains.
No family - You are screwed if you die before fathering an heir.
Vestisland (Iceland) - Dwarfy
Pros
Tiny ice-ridden island in the middle of nowhere - Hard to reach, enemies are limited by the size of their fleets. Takes two months to move an army from one province to the other by land. All mountains.
Vassal - Your liege is weaker than you and he only has one barony in his county.
De Jure Duchy - Technically you are part of the kingdom of Norway, though not actually. This means you get to vote on their crown laws and you can vote on their successors.
Norway is Elective - Norway is an Elective Monarchy.
Cons
Tiny ice-ridden island in the middle of nowhere - Bloody difficult to expand, your expansion is limited by the size of your fleets and your tiny island can support a maximum of four baronies between both of its counties. Iceland's growth opportunities are shot to all hell.
Vassal - Good luck getting support from higher ups!
De Jure Duchy - Norway gets a free CB on you for the whole game, and you can't set your own crown laws.
Norway is Elective - The Norwegian monarchy changes hands quickly, and frequently to good rulers. They are more or less an enemy, and if they conquer England they're a very, very close enemy. They also have enough ships to land 3000 troops on your shores, something made worse by the fact that...
Iceland Cannot Hire Mercenaries - You are too far away from anywhere for mercenaries to get there. Iceland's only recourse is to use personal or vassal levies. Good luck!
Also, an event will sometimes fire giving us the chance to embrace a heresy.
Pros
Not beholden to the Pope. Bishops always give you their tax money, no matter how pissed off they are - and since you can set clerical taxes to 50% that works rather well.
Holy War - Free casus belli on the whole damn world.
Cons
Not beholden to the Pope. Excommunication, Divorce, Invasion, Indulgences and Crusades are all no longer part of your game. It does cut off a lot of opportunities.
Holy War - The whole damn world has a casus belli on you.
Extreme Minority - That's you versus the full might of Catholicism. As in, literally just you and your Lord Spiritual. Those will be your sole converts at the start, and provinces do not convert with speed. Good luck!