The most important rule for roasting a tender and juicy chicken is to avoid overcooking it, as exceeding the target internal temperature quickly dries out the meat.
Achieving a tender and juicy roasted chicken is primarily dependent on cooking it to the correct internal temperature and removing it from the oven at precisely the right moment. Chicken, particularly the breast meat, can become dry and stringy very quickly if it's cooked past its optimal doneness. While factors like brining, proper seasoning, and resting are important contributors to flavor and texture, none are as critical as preventing overcooking. Overcooking causes the muscle fibers to contract excessively, squeezing out the natural juices and leaving you with dry meat. Always rely on a reliable meat thermometer to accurately gauge doneness, rather than relying solely on cooking time, which can vary based on oven calibration and chicken size.
Invest in a good quality instant-read meat thermometer to precisely monitor the internal temperature and pull the chicken from the oven as soon as it reaches 165°F (74°C) in the thickest part of the thigh, without touching bone.