If you are in MK for the day, watch the Electric Light Parade then exit out of the main entrance and then either take the boat right from MK to the Poly (the boat drops you off withing steps of the best viewing area) -or- take the Resort Monorail, then walk though the resort to the beach.
Check your times guide, but most nights Wishes are at 9pm
Option two would be to make a late dinner reservation at the Poly, say Kona or 'Ohana, and then stick around the resort until fireworks time.