The most important thing is to keep your pup on a loose lead. Try not to pull the pup tight to you. If you have to correct with a collar correction or pull back with a head collar, the leash MUST be loose again when the pup stops moving forward or is back in position. The attitude of the handler is very important - remain relaxed and calm. Don't act nervous or afraid - your pup will interpret that as you being fearful of an approaching dog, and that's not good. Be careful with corrections - if you are nervous or afraid, and your dog knows it, the correction may actually increased the anxiety in your puppy that a strange dog is approaching. The visiting dog will probably want to sniff the pup's rear end as a way of greeting - it's okay to let them do that. Your pup can do a little sniffing if the visiting dog remains engaged with your pup, but he must remain under control. After a brief visit, just give the command Let's Go and confidently move somewhere else.
We want pups to think that approaching dogs are not something to be worried about, but that they must also remain calm and self-controlled. The attitude and behavior of the handler is extremely important.