Richard Nixon changed Cold War diplomacy most notably by his efforts to open diplomatic ties between the United States and China. By doing this, he drove a wedge between China and the Soviet Union and, thereby, helped to improve relations between the US and the USSR.
China and the Soviet Union had once been close allies. By Nixon's time they were still both communist countries but they had grown apart. When Nixon opened diplomatic relations with China, he scared the Soviet Union. The Soviets thought that the US and China might ally against them. This led the Soviets to seek better relations with the US.
By opening ties with China, Nixon changed the dynamics of Cold War diplomacy and opened the way for detente.