How does the Inner Party help Big Brother maintain power?

According to The Theory and Practice of Oligarchical Collectivism by Emmanuel Goldstein, and also from O'Brien's conversations with Winston, we learn that the Inner Party maintains power in the following ways.
First, the Inner Party, which is about two percent of the population of Oceania, understands that it is in power for the sake of power and that it wants to stay in power forever. This group defines power as forcing people to do things they don't want to do and to live in ways they would prefer not to live. Above all, this elite want to maintain a rigid hierarchy, in which they are on top and control all the wealth and power. To do this, they have to keep people poor. As Goldstein's book explains:

For if leisure and security were enjoyed by all alike, the great mass of human beings who are normally stupefied by poverty would become literate and would learn to think for themselves; and when once they had done this, they would sooner or later realize that the privileged minority had no function, and they would sweep it away. In the long run, a hierarchical society was only possible on a basis of poverty and ignorance.

Therefore, the Inner Party ensures that Oceania is always in a state of war, in order to use up excess material goods that would otherwise increase ordinary people's standard of living.
The Inner Party also has abolished private property, so everything belongs to the state. The lack of private ownership increases the control of the tiny elite over people's everyday lives. In addition, the Inner Party uses technology to put people under constant surveillance, so no rebellion can form and no misdeed go unpunished. Further, the Inner Party has worked to destroy ties of love and friendship between individuals and families so that people's only loyalty is to the state. Finally, the Inner Party is dumbing down the language, removing all but the most essential words so that people will not have the ability to think complex thoughts.
It's important to note that there is no real Big Brother. He is simply a fictional figure the Inner Party has invented to represent the state, just as the Pillsbury Doughboy is a fictional character that represents Pillsbury products. As Goldstein's book says:

Big Brother is the guise in which the Party chooses to exhibit itself to the world. His function is to act as a focusing point for love, fear, and reverence, emotions which are more easily felt towards an individual than towards an organization.