You must explain that your fantasy is not to objectify your partner, or distance yourself from them. Rather, it's the opposite: a desire to take what's existing even further and become even closer to a partner. This is the first hurdle to get over when discussing a kink or fantasy with a partner. Wanting to try something new does not mean you're unhappy with your current expressions of physical and emotional intimacy. You want to explain that your fantasy is unique to them – it's something you want to do with them, not with someone else. They are the reason. They are special.
Second is having the inner acknowledgement that kinks are normal. Everybody has them. They are not sick, and you must have the confidence in yourself to know that before proceeding to talk with your partner. If you're comfortable and confident, there's more likelihood they will be too.
When you first discuss kinks with somebody, you should make the upmost effort to make them feel safe. Kinks and fantasies must be articulated in a pressure-free way. Use language such as "I've been thinking about...", "I've be wondering about trying..." and "Would you be interested in...?". To ensure your partner's emotional safety, let them know that you don't want/need to try this kink now, it's just something to put on the back-burner. It's something to think about.
It can also be beneficial to show others enjoying that kink or fantasy in a movie or TV show. No, not in explicit pornography – that's a little threatening to begin with. It's easy to find most kinks illustrated in regular cinema or television and Google can help you find them. By seeing that fantasy played out by actors, both you and your partner will have a more objective appreciation for trying it – call it the "50 shades" effect.
If and when your partner agrees to try something, take baby steps. If you're into, say, leather or lycra, start with something simple and non-alarming like a pair of underwear, not a full bodysuit or mask. It's vital that your kink it explored at your partner's pace, not the speed you'd prefer.
After-care remains paramount. Sometimes people experience an emotional low in the hours/days after trying something new in the bedroom. You must continually ask your partner how they're feeling, and really listen to their concerns if they have them. If they say "it's just not me", accept that and move on – there are more kinks out there to explore.
As with ALL types of sex, consensual is key when exploring kinks. You'll never see any kind of fantasy realised if you don't get enjoyment reciprocated by your partner.