Few things to keep an eye on. As loula mentioned, GSD are prone to eat infections. Since their ears are standing up, they have no defense against anything entering. Check some threads here, plenty of good recipes (Apple cider vinegar solution is one) that will help with the ear maintenance.
Sensitive stomachs affect an extremely small minority. Be cognizant of the food you plan on feeding. Again, check out the no-grain threads in the feeding my puppy section.
Hip/Elbow joints are something we all need to watch out for. The breed is known for having dysplasia. The growth period for GSD is rather long. The plates are actually open for a lengthy period. That being said, keeping your dog on the slimmer side early with healthy exercise (Limit constant running so as to not put unnecessary pressure on hips) will pay benefits later. Throw in some swimming when the weather warms up. That is a perfect exercise that does not involve any hard pounding of the elbow and hip joints.
Socialize your puppy early and often. Great idea that I've seen many people follow. Go to petsmart or your local, large pet store. Put the dog in the cart, and walk around the store. Get the puppy introduced early and often to people of all ages, other dogs.
Lastly, follow proper feeding instructions and do not worry every two weeks if your dog is a healthy weight or size. Some members here focus too much on worrying about if their pup is 0.3 lbs overweight or 3 MM shorter than expected height. They all grow differently.