Pawan's contribution is an important one, but from my experience I'll try and add a little bit more insight.
Trust. Obviously this is hugely important. If I'm letting you tie me up and do whatever with me, I need to have a level of trust with you initially. That's why I kind of kept my kinky side hidden from earlier boyfriends until we'd been seeing each other for a while. Probably it's also why the revelation of what I was secretly into seemed to scare a lot of guys off.
Communication. I want stuff from you, and hopefully there's stuff you want from me. A level of conversation, as well as understanding what we don't say goes a long way to making sure both partners are happy with a scenario. Show not tell can be a very powerful method of letting the other partner understand just what sort of thing you're looking for.
Empathy. For example when my husband puts the nipple clamps on me and makes sure they're okay before tugging the chain, but then he'll ask me sympathetically if it's heavy. Depending on the level of discomfort in my voice when I tell him yes, he'll know whether to go easy on me and remove the clamps early or to then say something like "awww, poor baby" and then attach some weights (which, when the mood is right, is sexy as hell, BTW)
Love, encouragement and gratitude. For some people, the love can be absent but I kind of need that. If not, then there should at least be some level of mutual liking and definitely respect for each other as individuals as well as for their roles. Encouragement, I feel, especially as a woman of size, having my husband tell me how well I'm doing and how much I'm turning him on is immensely helpful. You can sometimes get quite self-conscious when you're helpless and wondering what the other person is feeling. And gratitude, doesn't have to be overly pronounced, a simple "that was so sexy, thank you" will do it and work wonders for turning me on again when I'm thinking back on the experience later.
Honesty. A lot of people repress what they want. I know after keeping it a secret it can be really difficult to confide, but it's essential if both of you are going to enjoy sharing a kinky experience.
I'll add more if I can think of anything but right now I'm fixing my kid's dinner and trying to keep a secret of how incredibly horny I am