Remember that before your puppy is fully vaccinated, you can have your puppy meet dogs who are already vaccinated, but refrain from taking your puppy to public areas like the dog park, pet stores or training classes until they have at least had their 2nd vaccination.
It is best to take your puppy to a home in a controlled environment where you know the dog owners and the dogs. When you take your puppy/dog to dog parks, be cautious of the other dogs around you, you don't know if they are vaccinated or aggressive. If your puppy is attacked by another dog, that could be very traumatic for the puppy and difficult to overcome. In puppy socialization and training classes, make sure there is proper supervision from trainers and owners. As with humans, puppies can be shy, outgoing, timid, playful, or assertive. Allow your puppy to set the pace when meeting new dogs or people.