The thing that has worked best for me and D. has been trying to incorporate the two of our, um, interests together. By weaving his own fetish in with D/s, we have both come to enjoy things that neither of us expected we could enjoy.

I'm not sure if that would work in every case, but I think almost everyone has some kind of fetish or special turn-on. For instance, I had a roommate who was totally vanilla and conservative, but just adored guys in uniform (she couldn't get enough of movies with like Pearl Harbor). If you were with someone like that, you could incorporate the military thing into the BDSM thing by wearing a uniform and being her stern military man -- or, if you wanted her to be your Domme, by having her be your "drill sergeant."

The other really major advice I have is to do your very best to not make your SO feel like he/she is failing or disappointing you by not being into the same things. Everyone has their own hang-ups and difficulties, and a lot of people have had past experiences with sexual violence that might make it hard to adjust to a BDSM lifestyle. Pressuring them is the worst thing to do in that situation, because it can trigger a whole lot of bad feelings and associate them with you.