Well for the last few people I have slept with it really wasn't an issue. We knew what we wanted and there was no reason to talk about it.
When I go out and meet new people I always try and be honest about who I am and what I am about. What I usually tell a girl is that I'm not looking to settle down right now. I think this is a better what of saying "I don't want a relationship". To me "I don't want a relationship" says "I just want to fuck" too much. If she wants to know why or we start talking about relationships I will usually just say that my last relationship was really restrictive and I missed out on a lot of fun in college because of it. Something along those lines. I might go on to say that if I did date someone it would have to be with someone who would let me continue to be myself and not try and change me. I think this says several things.
1. Although I'm not pursuing it, I am still open to the idea of dating
2. I have high standards.
3. I'm happy enough with myself that I would rather be alone than with someone who didn't deserve me.
You might think that by admiting that you aren't really looking for a relationship you would turn off a lot of girls but I really don't think so. I actually think doing so makes you more attractive because you aren't a guy who needs a relationship to be happy. Also it puts you up on a pedestal making the woman have to qualify herself and work for you.
The other thing I try to do is to put sex in a possitive light. If we are on the subject I might say how I hate that there are double standards when it comes to sex and that I don't support them. I might also say that I admire a woman who is comfortable with her sexuality. I think this sets the mood. Now she knows that not only are you not going to judge her later on if things go down but you would actually respect her more as a woman for being spontaneous and unreserved.
If she is totally disgusted by what you say, forget her? At least then you know it's not going anywhere and you can go open other sets.
All of this is really just theory for me now though. I'm going to use it because I feel like it should work, but I will have to field test it before I can really say anything definitive.
