Before grilling the corn on the cob you should parboil the corn on the cob for up to 5 minutes in salted water.
Place the corn on the cob in salted water and parboil it for 5 minutes and then pat the corn on the cob dry and then place the corn on the cob on the grill and grill for 20 minutes turning the corn on the cob over occasionally.
The corn on the cob should be soft and golden brown in spots.