Track the Temperature
The most important thing is to know when your turkey is done, so a good thermometer is critical.
The best for beginners: a cord-style one specifically for grilling. Before cooking, insert the wand into the thickest part of the breast to the bone, and leave it in; a digital readout shows temperature and beeps when it's done.
Or, use an instant-read thermometer. The fastest and most accurate is the Super-Fast Thermapen. It gives you a reading within 3 seconds. Start checking after 1 1/2 hours.