A lot of people think 'Socialization' is dogs playing together. This is just a very small piece of socializing your puppy/dog. Socialization is the exposure to new sights, sounds, smells. Basically, it's giving your dog new experiences.
The prime period is a dog's life for socializing is 8weeks-16weeks. Take your puppy someplace new every day. You can go to a store parking lot and stand outside your car with your puppy to let them see, smell everything going on. You don't have to be in the thick of it--park way back from the store entrance.
Vets may say "Don't take your puppy anywhere until they've had all the rounds of shots" but they don't mean keep your dog in the house. Avoid dog parks and other places where there may be unvaccinated dogs, but DO take them out and about for the exposure to new things. Friends, family, neighbors with vaccinated dogs are a great resource for the dog-dog socializing. The ASPCA has a great socialization 'calendar' for puppies at http://www.aspca.org/pet-care/virtual-pet-behaviorist/dog-behavior/socializing-your-puppy
Give your puppy a leg (or paw) up by socializing them and you may avoid difficult behavior