Of course, this varies depending on which side you are talking about.
In general, the strategy of the Axis was to attack quickly and to try to win the war before the Allies really got themselves ready for war. This can be seen most clearly in the Japanese strategy in the Pacific. However, it can also be seen in Germany's blitzkrieg in Europe. Once the Axis had gained enough territory, they felt that the Allies would either be unwilling or unable to retake the territory.
For the Allies, the major strategy was "Europe first." The Allies tried to put most of their energies into fighting Germany. Once Germany was defeated, they would then go and fight Japan. The strategy against Germany was one of trying to pressure Germany on many fronts. The USSR kept the Eastern Front going throughout the war. The Western Allies later opened new fronts in Africa, Italy, and finally France.