The trick to a juicy pork tenderloin is a good rub and slow cooking.
If you can create a unique rub, such as a wonderful Asian-inspired one of garlic, soy sauce, and ginger, then you're on your way to being in a league of your own. Remember though: slow cooking means low temperatures for a longer time. It'll keep it oh so juicy. Always let your big meat pieces rest for 10-15 minutes to soak back up even more juices.