If it's a puppy, the absolute starting (training) rule is that the dog can never physically touch the cat (it must move out of the way of the cats; if a cat walks up to it, it must back away; if a cat is sitting there, it must walk around; it can never chase the cat, etc). This should get you an adult dog that would never think of a cat as an appetizer.
If it's an adult dog, same rule applies. If it wants to chase the cats, or shows too much interest (stares at or watches the cats), obviously discourage that behaviour (teach the dog it must avoid and move out of the way of the cats, and it cannot stare at them), but know you will probably never be able to trust them alone without you there (and sometimes even with you there). Unless you have a teacup Yorkie, it only takes one good mouthing to crush a cat, and that's tragic. Always lock up the dog when you are gone to protect the cats.
My dogs that were raised with cats from puppyhood (above method) never look twice at them, snuggle with them if the cats want to, etc., even though they are hunting dogs. They can be called off chasing stray cats in the yard. 100% safe.
My dogs that were not raised with cats unfortunately kill cats on contact, unless indoors. When indoors, they still want to go for the cats, but don't even dare look at them or acknowledge their presence, as they know we will have a "come to Jesus" meeting if they dare even think about it. I never, ever trust these dogs with cats, as I love cats
