score:28
Others (and perhaps myself) will no doubt expand, but the general outline was as follows:
Replace the nascent hierarchical feudal system of Anglo-Saxon England (and similar to contemporary French and German feudal systems) with an Anglo-Norman flat feudal system where every baron swears an oath of fealty directly to the Monarch, and only knights swear fealty to directly your Earls and Barons (the only two peerage orders immediately post-conquest).
Under the English feudal system, the person of the king (asserting his allodial right) was the only absolute "owner" of land. All nobles, knights and other tenants, termed vassals, merely "held" land from the king, who was thus at the top of the "feudal pyramid". When feudal land grants were of indefinite or indeterminate duration, such grants were deemed freehold, while fixed term and non-hereditable grants were deemed non-freehold. However, even freehold fiefs were not unconditionally heritableβbefore inheriting, the heir had to pay a suitable feudal relief
Allow those Anglo-Saxon Earls (of Mercia and Northumbria, Edwin and Morcar) who had not fought against him to keep their land provided only that they swear fealty to him directly.
Put down - harshly - the uprisings (Harrying of the North) that occur over the next decade or so.
the Anglo-Norman chronicler Orderic Vitalis wrote
The King stopped at nothing to hunt his enemies. He cut down many people and destroyed homes and land. Nowhere else had he shown such cruelty. This made a real change.
To his shame, William made no effort to control his fury, punishing the innocent with the guilty. He ordered that crops and herds, tools and food be burned to ashes. More than 100,000 people perished of starvation. I have often praised William in this book, but I can say nothing good about this brutal slaughter. God will punish him.
Build lots of castles (both royal and noble), initially as wood and later as stone fortifications, around the kingdom at key defensive and communication sites. These will serve as administrative headquarters; reminder of the "new order"; and garrison posts among other purposes aimed at both subduing the population and providing the "peace and good order" that wins over loyalty of the population.
From having almost no castles in the period before 1066, the country was quickly crowded with them. According to one conservative modern estimate, based on the number of surviving earthworks, at least 500, and possibly closer to 1,000, had been constructed by the end of the 11th century β barely two generations since the Normansβ initial landing.
Commission the Domesday Book to enumerate the kingdom and ensure that your tax collectors are both honest and competent.
Then, at the midwinter [1085], was the king in Gloucester with his council ... . After this had the king a large meeting, and very deep consultation with his council, about this land; how it was occupied, and by what sort of men. Then sent he his men over all England into each shire; commissioning them to find out "How many hundreds of hides were in the shire, what land the king himself had, and what stock upon the land; or, what dues he ought to have by the year from the shire."
This BBC article goes into some additional depth on the mechanisms of conquest