I make it known from the outset that I will not be tied down by her and that she is not my only source of gratification. They know that there are other women that I date on a regular basis.
It's easier to do it this way because it completely sets you apart...in a good way...from all the other guys she's ever dated. Most girls these days are allowed to hang out with other guys and not be looked down upon or disgusted at. However, most guys are NOT allowed to do the same. They get called insensitive, unappreciative, and a a-hole.
BUT if you let her know from the outright, first date preferrably, that you do actively see and hang out with other women, then you have given her two choices. One, to call you an a-hole and leave you in which case you refute back with "well, i'm not the insecure one here who wants to settle down after the first date....your loss and my gain". Second choice is that she stays and competes with these 'other' gals for your attention. In this case you refute back with "let's get our freak on".
Realize that you don't HAVE to be actively dating any other women at the time. Your date doesn't have to know. She just needs to know your attitude and mindset which should be one of spinning plates and dating multiple prospects.
It always works in your favor to tell the truth right from the outset. I prefer to do it indirectly because most women will get the covert message in this context. Either way she responds, it's your gain because you either filter them out or you keep them around with a higher interest level now.