Be sure your dog is healthy and shots are up to date.
Obey all the rules of the park.
Practice good dog manners and a solid recall before going to the park.
Bring only friendly, social, and relatively confident dogs to the park. Work on any behavior issues somewhere else.
Closely supervise your dog. This means keeping it in sight and monitoring its behavior to prevent any rough play or aggression and to see if it eliminates, so you can:
Clean up after your dog! (This should go without saying, but unfortunately it doesn't always happen.)
Bring young puppies who haven't had all their shots. Most parks have rules regarding the exact age that puppies are allowed, but a good rule of thumb is four months old, and their shots need to be up to date.
Bring your dog if they don't enjoy the dog park or have aggression or socialization issues. You need to work on this before taking your dog to the park for a romp.
Bring treats to the dog park. This can encourage bad behavior from all the dogs.
Bring small children to the dog park. They usually don't know how to interact with dogs very well, and the dogs in the park may not react well to them, either.
Following these tips can make the experience positive for you, your dog, and everyone else in the park.