If your dog is still young, socialization is key. Take him/her around people as often as you can. If he/she is older and not properly socialized around people, it may take a little more time and effort. Start by taking your dog around people you know and have them hand out treats to show that people are "okay."
I agree with Puppyluv. Socialization i extremely important. In addition, some shepherd tend to have a more timid personality, so try to pick one that is naturally outgoing. Pay particular attention to the home as well. Shepherds are protectors, so have people come over often (or practice with the door) and teach them that strangers in their territory are okay. See my hubs for more training/ socialization info.