There're many reasons your turkey breast is dry, but the common ones are overcooking and over-brining. Yes, brining helps to bring some moisture to the white meat, but a long time in a salt solution won’t mean a juicier meat. Therefore, I suggest brining turkey breast for no longer than 4 hours for smaller pieces and up to 7 hours for larger breast pieces. Also, it's easy to overcook your meat. Using a thermometer is the best way to avoid this. When your turkey breasts are almost at 165F (74C), it's time for broiling. By the time broiling is done, your turkey should be perfectly cooked. Let the meat rest after it's out from the oven to give some time for the liquids to distribute evenly inside before slicing.