So long as you follow some key principles such as early socialization, regular short and engaging training sessions with plenty of positive reinforcement, praise.... (wileypup.com)
But sensitive breeds such as German Shepherds need careful introductions to new people and places, and plenty of positive reinforcement for appropriate behavior, until 2 - 3 years of age. (germanshepherdcentral.net)
This being the case, you will need to train your dog with a firm and consistent hand — use plenty of positive reinforcement to cement his training. (petguide.com)