When should I take my dog to dog parks?

There's no rush! If that's your only option for socialization, make sure you start slowly and at your dog's pace. Prior to attending a dog park, make sure your dog has a good recall and has practiced getting to meet different types of dogs (not just size & breeds but play styles and demeanours) in more controlled environments. This will better prepare both you and your dog for this type of unregulated environment.