How do i train my dog to be non-aggressive towards other dogs?

I have had Bruce, our 9 month old pit bull/ lab mix for about a month or so. When ever we take him out for a walk and there's another dog he just goes ballistic! Like he would want to attack. We do have a choke collar on him and it definitely helps, but it obviously isn't fixing the problem.... Anyone have any major tips or advice to give on how to socialize him properly and to help with his aggressiveness?