All of my current partners were already active in the kink community when we got together, so it was never an issue...

My girl was already interested, so it was exactly like 'I hear you're in need of a Master. I'd like to apply for the position.' she said yes, I told her to go forth and masturbate, and that was that.

For your boyfriend, I'd take it easy. Start with some bondage (either you or he being tied up, whatever takes your fancy), and then introduce some spanking. If he seems to be interested, then start a conversation about it.

I didn't really convince him, so much as we went to the sex toy store together and we both stood next to the bondage stuff and said .... that could be fun. Broke the ice, we bought it, and started from there.

Communication and active imaginations?

I had an idea that I was a sub, but Master already owned his Dom thing and just pointed me in the directions he wanted - ask permission to masturbate, sleep in my cuffs if I've been really bad, photo-shoots every now and again. The very first thing we did was orgasm control - like the asking permission or not being allowed to until such-and-such was done or obeying directions during phone sex. It's difficult to keep up a proper D/s dynamic with long distance (different countries), so we mostly do a lot of talking out about expectations, comfort level, and ideas for the time being.

I think ... giving him time to adjust to the idea would help a lot. Do one thing, talk about it, etc. See where it leads.

Our sex life was starting to become boring and monotonous so an online friend of mine introduced me to Fetlife and I fell instantly in love with it. I spent a while going through groups and reading up on some things before I asked him to join up with me and see where it went. It took him a while to become comfortable with the idea of joining but once he did he was hooked just like I was. That was about 2 years ago and we're having so much fun with our 24/7 D/s relationship and all that comes with it.

Just whip out some toys and see what happens!