In "The Prince," what does Machiavelli say is the best way to maintain hereditary, mixed, civil, and ecclesiastical principalities?

On heredity principalities, Machiavelli says:

"I say at once there are fewer difficulties in holding hereditary states, and those long accustomed to the family of their prince, than new ones;" (Machiavelli, pg. 10) 

Here he suggests that hereditary principalities are easier to maintain because a ruling family develops a relationship with the people and unless the ruler exhibits some extraordinary vices, the people will continue to love him.

New principalities are harder to govern, Machiavelli states. The new ruler must conquer territory in this process he will make enemies.  He must make his enemies in the new territories his allies by giving them something to make them happy.  It is also important for the new ruler to live in the conquered territory, so that he can observe problems, solve them quickly, before they become unmanageable. 

"in entering a province one has always need of the goodwill of the natives." (Machiavelli, pg. 11)

In a civil principality, an ordinary citizen can become a ruler with the help of his fellow citizens. 

"one ascends to the principality, or when by the favour of his fellow-citizens a private person becomes the prince of his country." (Machiavelli, pg. 25)

This leader must stay in close contact with the people that put him in power, and not get too close to the nobles.  He should always seek the goodwill of the people.