Looking for tips and advice on how and when to approach the subject of keeping things casual with women.

Bit of background: I'm an attractive guy in looks, personality and career and my female friends all say I'm a catch. Because of this I've never had an issue attracting girls and don't have to work too hard to get them (cry me a river, right?)

My problem is that I can be too passive, just go with the flow and end up sleeping with women and dating them for a bit...which is great until you end up hurting some because they thought it was more and because we never had the chat early enough, and that's not good and bit of a shitty thing to do.

I want to casually date, not just necessarily hook up, but how and when do you have this conversation. I guess it should really be before you sleep with someone but at what point? And how do people bring up the subject? I want to be the one who initiates the conversation. At the moment unless it comes up in conversation early on, I just go with the flow.