The advice from the previous poster is just what I would have said...so I'm just going to share a funny housebreaking story instead.
My best friend was given a puppy as a gift from her boyfriend. After every nap, meal or play session Cindy would take Nadia to the door, sit her down, put on her leash and take her for a potty walk. Nadia is a very smart dog (chow/cocker mix) and soon caught on that if she went and sat by the door she'd get to go for a walk. ;-)
I went to visit Cindy and stayed overnight. Everytime Nadia went to the door, Cindy dutifully got the leash and took her out for a short walk (just down the street for a house or two). Cindy spent more time walking than visiting...it was very funny!
Eventually, Nadia didn't need quite so many walks and now, years later, Nadia is very well housetrained, and she LOVES walks!
:-D Bettina

PS - if this is a small dog, you could always try the new "dog litter" from Purina.