Look for a nearby dog training school. That is the best and safest way to go as they will and should group puppies accordingly based on their age, size, demeanour, and play style. For environments where categorization isn't possible (perhaps because not many puppies of a similar age group are available to attend), you will want to make sure that you can attend the socialization sessions to ensure your dog is participating in safe and enjoyable for him/her.
If your local training school doesn't offer socialization/play sessions for puppies, you can consider your local doggy daycare as they tend to provide play sessions for young dogs as well. Just make sure that they're properly supervised and short so that you can slowly increase the amount of time prior to having your pup attend regular daycare sessions. Do your best to avoid dog parks! Though we could write a lengthy article on why to avoid the dog park and/or what to consider before attending, we think that puppies (and most dogs under 8,9, 10 months) and their pet parents are likely not ready to attend unsupervised, busy dog parks. In the pet training industry, there are too many different takes and views on handling and raising and that's okay. But what you want to prioritize more than anything is your dog's physical and mental well-being!