Positive reinforcement at all times! Any time they do something desireable.. praise, praise, praise! Be gentle in correcting any negative behavior, if any. And socialization... the more socializing you get him/her to do, the more confident he/she will become. Start slow, and don't let people rush him/her, especially small kids, or people with dogs that aren't controlled. If you have friends/family with similiar personalities, setup playdates (as long as everyone is vaccinated) and in a controlled environment, allow them to play, maybe once a week for about 10 minutes to start. Then build up the amount of time they get to play. Over time, you'll see the pup's confidence building.