Cats that as kittens had positive experiences with dogs will usually adjust more easily to a canine housemate.
Confine the first pet to one part of the house while the new pet explores the rest. Then switch their territories. This allows each to become familiar with the other's presence and allows the new pet to locate places to hide when conflicts occur.
Put a leash on your dog. If he attempts to chase or back at the cat, give the leash a quick jerk and tell him "NO" firmly. Praise your dog when he behaves calmly around your cat. The cat will soon learn that if she doesn't run, the dog won't be inspired to chase her, and your dog will understand that harassing the cat is not allowed.
Ensure that the cat always has access to hiding places the dog is not able to reach. It is wise confine them separately at first when you are unable to supervise.
Spend ample time with your original pet to minimize jealousy of the newcomer.
Let the two pets set their own pace and ease into the relationship. Do not force them together. They may take two or three months to come to an understanding.