I grew up with Shepherds, and have had them all my life. My family used to breed them, so I think I know a lot about the breed. Here are the most important things to do, IMO.
1. Make sure the dog has all it's shots.
2. IMMEDIATELY take the dog to obedience school.
3. IMMEDIATELY take the dog to "social events". Remember, you want a dog that can protect, not that is over protective.
4. Buy the book "The art of raising a puppy" There is a great website for working dogs
http://www.workingdogs.com/book008.htm
5. Do you have kids? If so, get all of your kids friends over as early and often as possible. This also goes for your friends, but not as important. Introducing the dog to any and everything is the key.
German Shepherd are the best dog on the planet, IMO. You just have to be sure the dog is trained and controled early. I have seen people who can't handle their shepherd, and it's not good. I have a neighbor who's shepherd is constantly barking at kids coming over, or at other animals. My dog literally just sits at attention until she is told to do otherwise. My dog is a large breed shepherd that weighs 123 lbs, and not one person on the street is affraid to come up to him. My neighbors dog is fairly normal at about 75 lbs, and constantly barks at everyone.
The only time my dog has ever "acted up" was when a meter reader came into our backyard. First of all, they aren't supposed to do that if signs of a dog are posted. Anyway, he went back there and ran into my dog, and freaked. He started running, and my dog barked and snarled. He froze, and I walked outside and said "ausrushen" or relax in German. My dog sat down and stopped immediately. I fully expected to have a big hassle on my hands about this, but I never heard a word about it.
My point is, make sure the dog is well trained, or you could be in for all kinds of issues.