What should I do if my dog barks and lunges when we encounter other dogs?

One of the first things I'm going to do in that situation is make sure I have the proper equipment to walk this dog comfortably. I would not use a prong or pinch collar because I don't want any pain associated with what the dog is seeing. If a dog sees another dog, and then I have a pinch collar, that pinch now teaches the dog that every time they see another dog, they get pinched. Instead, I would use a head halter or harness to make sure I have control of that dog. Then, as soon as that dog sees another dog, I would redirect their attention toward me and increase my distance from the other dog as I work on a positive reaction with my dog. I would keep doing that until I've built up enough practice that I can have my dog see another dog, look at me for a reaction, get a treat, and then walk away.