Go outside with him and praise him each and every time he eliminates. Housetraining should be based on the prevention of accidents rather than discipline after the fact. Since your dog is no longer a young puppy he will have better bowel and bladder control. Place the dog on a regular elimination schedule and take him outside at certain times, whether he needs to eliminate or not - first thing in the morning, after meals and play and the last thing at night. It is essential to accompany him to make certain he is, indeed, eliminating.
Dogs are creatures of habit.
The more quickly you turn a good behavior into a habit, the faster your training will go. If you haven't already decided on a crate for your dog, you may want to investigate purchasing one for him. The most effective way to teach him to eliminate outdoors is to prevent him from using the house in the first place. Dogs are den animals and have an instinct not to soil their den. The crate will become your dog's den.