If you are introducing a new dog to a home that already has a cat, your cat will need time to gain confidence around the new arrival, even if you've picked a breed with a better reputation for getting on with cats. Both animals always need a space of their own, with the cat especially needing somewhere that's out of bounds to the dog, with a litter box and food and water to hand.

The introduction
Cats will normally react to dogs by hissing or swatting with their paws, and will try to escape by running or hiding. They may also spray to mark 'their' territory. But with time and patience feline-canine harmony should be achievable. Although never leave the two unsupervised until you can completely trust them to behave in your absence. 

• Pay attention to both pets as often as possible. Often your attitude and attention is enough to prevent serious rivalries or hostilities from developing.
• Settle your cat in a room with an upward escape route, such as a tall cat-scratching post, a windowsill, a shelf, or the back of the sofa. This should never be your cat's 'favourite' room, or the room where his or her bed is located. Pick a neutral area outside your cat's 'territory' Shut the windows and doors so the cat can't run away - it's best that they confront their fears as soon as possible!
• Now bring in your dog. The cat will almost certainly leap up to a place of safety.
• After five minutes or so, take the dog away and let your cat leave the room as well.
• Repeat these short introductions. Eventually curiosity will mean your cat won't be able to resist a face-to-face introduction. 
• Cats won't make contact with dogs that torment them, so if this looks like happening call the dog to you. Always signal an emphatic 'NO' if your dog is at all unfriendly or tries to give chase.
• Make sure your cat gets plenty of opportunity to stalk and pounce on things other than the dog's tail.
• If you have brought home a particularly boisterous puppy, keep it in a puppy crate while the cat takes stock. Keep the introductions short, but frequent. 
• Try giving treats to your cat, to associate the dog's presence with tasty rewards.
• Separate cats and dogs at mealtime so both can eat in comfort, and won't get tempted to investigate what's in each other's bowls. Cat food is not suitable for dogs, and vice versa
• Make sure your dog does not have access to your cat's litter box. Sooner or later, the dog may attempt to eat its contents!

Kittens
Kittens usually love dogs, whilst dogs find kittens unthreatening. But just like adults, they need to time to adapt to the new arrival. Introduce them gradually and never leave them alone together until a pattern of good relations has been established. Some adult dogs will carry kittens around and young kittens will accept this attention, but it's probably best to gently take your kitten away from the dog to avoid injury. A bite from a dog can be fatal.

Finally, don't worry if they never really get along. Cats are naturally independent and can do without having a dog for a friend, thank you very much! As long as each has their own space, things will work out fine.