What role do the contradictions (war is peace, ect.) in 1984 serve on a grand scale? What are some other contradictions besides the party slogan and doublethink? What role do the contradictions serve in the framework of doublethink and how does doublethink serve the needs of the party?
On a grand scale the contradictions all serve to help the Party control the general population. Take "freedom is slavery" for example. The people think they are free, because that is what they are told by the party. But in reality they are slaves to the Party's wishes. The "ignorance is strength" Party line is especially controlling. If the people are kept ignorant, the Party gains strength and control.
Doublespeak and doublethink are both tactics that the government is using to control people. The government is telling people that doublethink is allowing them to think more, but in reality it is the government telling them what to think. Doublespeak serves the same function. Doublespeak is the government's ploy to get rid of a lot of words in the language. The government says that it is streamlining language, but in reality they are eliminating anti-party language. Additionally, with fewer words to choose from, the population has fewer ways to express their ideas. No way to express an idea? Then the idea might as well not exist. All of those contradictory ideas are being used to dumb down the population and make people more pliable to the needs of the party.
You asked for another example other than the party slogans and doublespeak. I would say Winston's job of changing history to affect the present at first seems contradictory. How can rewriting a history book affect the present and future? But Winston will eventually learn that control of the past is control of the future.