If you are REALLY nervous, try setting up a meeting with a friend who has a dog, and have the dogs meet with a gate or chain link fence in between them. E.g. have your friend meet you in a fenced-in tennis court or baseball field, then one of you can be outside and the other inside. Then you can have the dogs sniff each other through the fence and see how yours reacts, and if all goes well then you can bring your dog onto the other side and have them continue their sniffing on leash.
while out on walks if you are just passing other strangers and their dogs, you don't have to let your dog interact with the other dogs if you don't want to. (in fact many people may prefer that their dogs don't meet others as it interrupts the flow of their walk...) but if you DO want your dog to interact with others but are nervous about it, then I suggest first doing several of the above meetings with the gates with different friends/dogs so you have a better idea of how your dog is likely to react when meeting new dogs, then you may have more confidence about letting him meet new dogs on the street. Or you can join a class for the socialization experience so he can get practice in meeting other dogs while still in a controlled setting and under the eye of a trainer.
