Take the dog out A LOT! Tell the dog to go *insert word* (potty or whatever you chose to use) and when the dog goes, praise the h**l out of it. Tell the dog good girl (or boy) and use a happy, silly voice. You can also use a piece of it's puppy food as a reward.
I worked with a Labrador Retriever Rescue and had about 25 Labs in my house over a five year period. Trained quite a few of the rescues as well as my two Labs.
Feel free to PM me if I can help you further.
Good luck with the puppy!
