The secret to making moist chicken breast is to cook it at a lower temperature than usual. A lower temperature results in a more tender chicken and allows the juices to redistribute through the breast. In addition to moist meat, cooking chicken at a lower temperature reduces the chance of the meat drying out. A good rule of thumb is to cook the chicken breast against the grain, which helps retain more juices.
Make sure your chicken has warmed to 165 degrees Fahrenheit inside. Overbaking should be avoided because it will make the meat dry.