Follow the advice of your vet, and your puppy will likely be just fine. They often get it from drinking contaminated water. Try to keep your pup from drinking from stagnant puddles and gross looking water. Washing and sanitizing food and water bowls regularly is a good idea, too.
My puppy had a case of giardia this past fall...just follow the medication instructions, wash any bedding/toys that you can, and clean well if they have any accidents in the house. My pup got over it just fine, and neither of our other dogs got it. I think it's an easy thing for puppies to catch since their immune systems aren't fully developed. Also wash your hands well after cleaning, since some strains can be spread to humans!