What i've done is put the cat in a carrier and bring the dog face to face with it. I held the dog down so he wouldn't be jumping around or anything. Just to get used to each other's scent and not close enough that the cat could actually swipe at the dog. As they get more used to each other, I've held the cat down, very carefully, and had my older son bring the dog closer (and held so the dog can't struggle or get away) so both animals are in close proximity, but neither can do anything about it. That has seemed to help. At least for our more outgoing cat. The skittish cat, I never bothered with because she almost never comes out of the bedroom anyways.