I think the main thing to remember is that they don't communicate the same way.

When I adopted a dog into my home which already has a cat I introduced the dog gently. Helped my dog becalm around the cat and eventually the cat warmed up to the dog.

In this scenario I actually took the time to train my dog to help my cat. Of course I also took the time to show my cat that the dog can be trusted. Mostly I just trained my dog to leave the cat alone. Any time she wanted to rush up to my cat I would start playing with the dog, do some tricks, distract her so the car can just watch until the cat started getting curious to what we were doing.

And you know I think it's okay if they aren't friends. Some people don't like certain personalities and I imagine this is the same.