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.
(continued from previous answer)
"now to speak of ecclesiastical principalities, touching which all difficulties are prior to getting possession, because they are acquired either by capacity or good fortune, and they can be held without either; for they are sustained by the ancient ordinances of religion, which are so all-powerful, and of such a character that the principalities may be held no matter how their princes behave and live." (Machiavelli, pg. 30)
Machiavelli suggests that ecclesiastical principalities are easy to maintain because they are governed by religion. The authority of the leader comes from God, so it is not questioned by the governed.
look on pages 34, 36-37, 63-64, and 69 for complete answers