Selecting: The first step to great grilled corn is to select young, tender corn. Old, dry corn is not going to be good no matter how you cook it. Young corn is loaded with sugars that are going to caramelize on the grill giving your corn an extra sweet flavor. When selecting corn on the cob look for bright green husks, lightly yellow stalks, and the ends of the silk should be lightly brown. Now peel back the husk enough to expose a few rows of kernels. The kernels should plump and translucent.
Preparation: Once you have the corn you are ready to prepare them for the grill. Some people will tell you to leave all the husks in place. This will protect the corn from the fire, but it will also trap in all the moisture, steaming the corn and preventing smoke from getting to the corn. So, remove all but a few of the layers of husks. You want at least a double layer of husks over the corn but not much more. This will keep the corn from burning, but also allow excess moisture out and smoke flavor in. Actually the husks will burn, creating smoke that can then sink into the corn.
You will also want to leave the stalk intact. This will give you a good handle for later. Remove as much silk as you can, but you don't need get it all out at this point. Once grilled, the silk will be easier to remove.
Grilling: Now you are ready to grill. You want a medium high heat. Hold your hand about five inches from the heat source. You should be able to keep your hand there for a count of three to five. This is a good heat. Corn on the cob will take about ten minutes to grill, turning every two minutes. The husks will burn, but the kernels of corn shouldn't. Watch for the kernels to turn a golden yellow color.
If you can't find corn on the cob with the husks still on, blame industrialized farming and use a baste of flavored butter to keep the corn from drying out. Avoid sugars in your baste because it will burn on the grill and turn your corn black. Always remove corn from the grill before it starts to turn a dark yellow color. This is the first clue that it is beginning to burn. With corn it is better to undercook than overcook.
For an additional variation you can pull back the husks completely and coat the corn with a flavored butter mixture. This will add extra moisture and flavor to the corn. Always fold the husks back into place before you put the corn on the grill.