My favourite way of teaching a dog to behave on lead is to go to an off leash park, walk around the perimeter and stop and use treats to get your dog to focus on you, "sit","stay" "look" etc etc.... then move closer... pause when you get to dogs that are at the fence.... if your dog reacts, turn around and walk away... start over again until you can get next to the fence and your dog is happy to be close to other dogs. Generally, alot of the opposition to other dogs has to do with protection, if you were off lead it would all work, but if that is frustrating for you (as it is for me!) get them to obey before putting them in the stressful situation, and then inch your way closer until they behave in an acceptable way for you.