To grill moist, juicy chicken, use an instant-read meat thermometer. Whether you are grilling boneless breasts, bone-in pieces or a whole bird, the idea is the same: cook chicken to a safe internal temperature—but don't overcook it. The leaner the chicken, the more easily it will dry out.
The USDA recently revised their recommendations to simplify their safety guidelines: they now say 165F for all cuts. (The previous guidelines called for cooking breasts to 160F and whole birds to 180F).
I still cook chicken breaststo 160F, at which they are safe, tender—and not dry! I cook dark meat chicken such as thighs to 170-175F-- at which point they are safe, juicy and appealing. (Thighs are safe at 165F, but the texture is a little rubbery and the meat may be pink, especially near the bone.) For some tasty grilled chicken recipes, see Grilled Chicken Meals--Hot Off the Coals.