Sounds like you have a dog who wasn't exposed to much as a pup or one that was taken from mom early. In any case, he is scared, and you need to show him that it's OK! He needs to learn to TRUST you. Get some yummy treats and start working on very basic stuff like sit, down, etc. Watch me is a command I taught Loki basically by starting with the food by my eyes, and then lowering it but waiting for him to look at ME and then saying YES and giving him the food. This works great for walks.
Don't pacify him because that just tells him it's OK to be afraid. But if there's something he's afraid of (for Loki it's thunderstorms) that's when you get up and say "lets do some tricks" and head into the kitchen or wherever and get your treat jar and start working on stuff. Loki barks at "scary" dogs when he is outside so when he does I call him in the house. Now he tends to just bark once or twice and then RUN in the house and go sit by the treat can
There are a lot of great books out there to help you. Check out authors Pat Miller's book for training (they shouldn't overwhelm you) and Patricia McConnell's books for inspiration. It also wouldn't hurt to sign up for a POSTIIVE reinforcement class (you know it's that when there is no collar jerking, no yelling, no "punishment" beyond a time out... you'll hear things like "reward good behavior, ignore bag behavior" The dog only knows what he needs to do to get attention so you only give attention when he behaves! That sort of thing, with lots of food and praise rewards!) Don't go to a Cesar Milan inspired or "old-school dominance" type of class especially with this type of dog. He is already scared he needs to learn to trust you not to fear you.
Good luck!