Ask at your vets if they do a pre vaccination puppy group. You can also take him out up in your arms to meet people and see stuff and invite people to your home to meet him. Just keep him away from dogs you don’t know. Take its steady. Socialising “the more the merrier” can be too much for most pups, make sure he gets his rest and quiet periods as well as outings. Be patient, be patient and then be patient again. If he makes mistakes its your fault not his. NEVER smack, shake, “Alpha Roll” or shout at your puppy.
Here’s a decent book
Amazon.co.uk User Recommendation
A decent training class can be good but make sure its a decent one, I chose the wrong one and it took months to undo the damage. It wasn’t cruel but it was too loud and bright and pressured for my boys. Ask to go without your dog and watch a class. If they refuse then don’t go any further, if they do allow you then what do you think of the class? Is it calm with small numbers and lots of fun and praise?