Dogs express their fear in different ways. They may bite or scratch, run and hide, tremble or even urinate when afraid. Your job is to figure out what's scaring your dog and help ease and overcome his fears.
Determining why your dog is fearful isn't always essential to treating the fearful behavior, although the reason for his fear will dictate the relative success of the treatment. A dog that is genetically predisposed to general fearfulness, or a dog that was improperly socialized during a critical stage in his development, will probably not respond as well to treatment as a dog that has developed a specific fear in response to a specific experience.
It's essential, however, to first rule out any medical causes for your dog's fearful behavior. Your first step should be to take your dog to your veterinarian for a thorough medical evaluation. Most fears won't go away by themselves, and if left untreated, may get worse. With time and patience, most fears can be treated using desensitization. Speak to a pet trainer for assistance. To desensitize your dog, repeatedly expose your dog to low levels and for a small amount of time to the stimuli causing him fear. Reward your dog with treats and praise for his calm behavior in the presence of the stimuli. Gradually increase the exposure to the stimuli. As long as he remains calm, reward him with treats and praise. If at any point he becomes anxious over the stimuli, remove the stimuli and proceed at a slower pace. This process may take a long time. You should proceed at a slow enough pace that your dog never becomes fearful during the desensitization process.
Smart Tip: If you have to drag your dog to the car or he trembles uncontrollably during the ride, ask yourself whether you take him in the car only when he has to go to the veterinarian or kennel (or somewhere else that he might find unpleasant). If the answer is yes, take him for a ride around town or go somewhere pleasant, such as a playground. Do this several times so that he gets the idea that a car ride doesn't always lead to a scary place.