Although MacArthur was not the only one responsible for this, the main strategy used by the US in the Pacific was one of "island-hopping." The idea here was that not every island held by the Japanese had to be attacked and conquered. Certain islands (or places on huge islands like New Guinea) could be attacked while those areas "behind" them could be left to "die on the vine."
So the US attacked generally northwards towards Japan, taking some islands and leaving others untouched. One example of this is how the huge Japanese naval base at Truk was never invaded -- it was bombed repeatedly, but never actually invaded.
The strategy was known as "island hopping". The United States needed to move closer to Japan in order to effectively strike, however it was not necessary to defeat the Japanese in every territory they had overtaken. By picking an choosing islands strategically, we were able to encroach upon the Japanese without over-expending our military forces.
One of the largest aspects of the campaign was called island-hopping. Rather than trying to take every single fortified island, the commanders in the Pacific identified each step that was necessary and bypassed some very heavily fortified bases knowing that they could control shipping lanes and other avenues of approach and basically starve out those garrisons rather than taking them on with costly invasions.
In doing so, they also moved to position themselves for the final assault on the home islands as well as putting themselves into a position to bomb the Japanese mainland with bases in places like Saipan and Iwo Jima.
The campaigns to take these islands tended to be very bloody frontal assaults on the beaches as the Japanese had become experts at fortifying the rugged coral islands and the fighting to take them was intense and very costly.