I'd never give details of my sexual past and I'd sure hope to God that my SO wouldn't either.
Couple of things to do...
1) If you are between SO's, throw out or hide any toys from your old relationship. If you do want to re-introduce them, make sure they are in new condition and present them as new. The last thing I'd ever want to see is my SO with a hidden sex swing in her closet that looks like it's had 100,000 miles put on it.
2) If you are talking about what you like and dislike, position it as "I've always wanted to..." or "You know what sounds fun?...". Stay away from "Well Ted used to throw my legs up over my shoulders and lift my ass off the bed while he powerfucked me."
3) If your SO asks you if you've ever done so-and-so, even if you've done it, just respond with what you'd like to do with them... not what you've done. Example: "Hey hon, did you ever give your ex a pearl necklace?". Answer: "Wow! The thought of doing that with you really turns me on. Are you game?" Alternative Answer: "We have so much fun together that I really don't see that as something we have to do unless the idea turns you on."
4) And if your SO is just *obsessed* for details, just tone everything down. Understate everything... Also, girls especially, if you have done some really "out there" things with an ex and your SO knows it, talk about 1) "How much you really thought you loved so-and-so" and 2) "How being with your current SO had taught you how you can care even more about a person". For some reason, we guys can justify you doing some kinky stuff if we tell ourselves you thought the guy was "the one". Just make sure that we know we're even better than "the one" ever was!
5) Also... ladies especially... it's really fine to make a guy you're dating wait even a month or so before sex. But here's the kicker... if I've waited 45 days and nine dates before we have intense sexual contact, please, please, please don't let me find out later that I'm number 45 on your roster -- especially if you are 25 years old! I'll do the math and realize you couldn't have made all those other guys wait 45 days
6) And finally... if you're doing some naughty stuff with me... especially deviant stuff... even if it's old hat to you, just make casual comments that will help me live the lie that I'm first. You know... "I just could never see myself doing XYZ with anyone. But for you, because I know you like it, it just seems natural to me."
Anyway... that's my 2 cents!