If you are in one of the parks getting to another hotel is easy, just hop on the bus for the resort you want to go to. When you are finished at the resort, as Tyler states above then just get on a bus for one of the parks that is closest to your resort, once you get to the park just get on the bus for your resort. It can be time consuming.
If you want to just go from resort to resort, I have found that it is easier to pay for a taxi, especially if we are running late(which we usually are).