Dogs might have fear related anxiety for numberous reasons and regardless of why they are suffering (trauma, lack of socialization, etc) there's a lot you can do to improve your pet's quality of life.
Start by making a list of things your dog is nervous or anxious about. These things can include anything from strangers to other dogs to stuff animals to vacuum cleaners. Anything your pet shows discomfort around can be on the list.
Teach your pet some fun tricks that keep him/her moving so they have a distraction when the scary thing/event is happening. I love hand targets, spin, loose leash walking, chase (dogs chases you), jumping, etc. This gives your dog something else to concentrate on.
In Where's Your Sit's Confidence Booster class we teach the dogs the tricks and then introduce low level scary stimuli like a dog across the room or a weird noise. As long as the your dog is able to keep eating and "playing" then they are learning to tolerate the scary event. Make sure to start really slowly (this is where working with a dog trainer would be helpful).
Allow your dog to look at the scary thing and then reward with a tasty treat when he/she looks back at you. Try to keep sessions very short (less than 5 minutes) and keep your attitude upbeat (but not over the top). The more your dog is exposed to scary, new stimuli that doesn't hurt them and that is paired with something fun like games and food the quicker their confidence will increase.