I played as Count Northampton in my current game (1066 start). I rode out the Norman and Norwegian invasions building up my war chest(they never went after my county) and they eventually petered out and lost their wars. I fabricated claims on the independent Welsh counties and duchies and attacked (hiring the 75g mercenary bands to augment my forces). The King of England also made me the Steward and gave me the Duchy of Oxford so I built up a decent demense in just a couple decades. After that, I fabricated a claim on England (using the plot, got the English spymaster on board giving me a huge bonus). I sat on the claim for awhile until the current king died, then the new king immediately folded to a faction that put Duchess Lancaster on the throne. Duke York would have none of that crap though and made a faction to put me on the English throne. I joined up with that and Duke York didn't waste any time making his demand to the new Queen, who laughed us out of the palace and so we went to war. It was a long and bloody conflict but we came out on top (Duke Kent wasn't happy either and ended up going indepedent for awhile during that war).
Once the English crown lay atop my head, I changed the succession to elective and voted for my genius grandson as heir. When he became the King, he expanded and took Ireland, and slowly whittled away at the Norwegian and Scottish territories until finally getting enough to call himself Emperor Britannia. He then married the lusty Queen of Hungary, lost a leg fighting one of her wars (that was later healed by a benevolent boar when he decided to hunt the feast meal by himself), fathered 12 children, and went insane, but that's really a story for another day.