Socialization is not just about exposure (i.e. just seeing, experiencing new things) your pup has to have a good time doing it.
Make new experiences fun, positive and relaxed.
Go at your dogs pace - respect their threshold, dont force proximity, interaction, etc
Offer praise and make it rewarding - take some high value treats along to make things extra special
If you're puppy is particularly shy, fearful or overly excited - leave the situation and consider reaching out to a professional who can give you some new tools and skills to help your dog
For a great article check out: https://dogsaholic.com/puppies/puppy-socialization.html
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