I'm friends with several girls I've been with and/or dated. With each of these, I did the following:
Firstly, DON'T lead them on to think you're down for more, or something other than, you really are (as far as exclusive relationships go).
Secondly, don't sleep with them too often or spend too much time with them too soon. This will cause them to get overly attached - especially young gals.
Thirdly, be nice to them afterwards. Hang with them in social situations. Like and comment on their facebook statuses in a friendly way. I know it's dumb, but it works. If you dated them, not just hooked up, give it a little time before you start this.
Fourthly, be descret! Kissing and telling is for chumps. They'll respect you more if you can keep a secret. They're going to tell their friends anyway, so word will get out...especially if you are any good!
That said, I do have a bit of a reputation as a player (even a cheater) but am well liked and have a lot of female friends who think I'm a dog, but it's endearing not offensive.
The ones who don't like me are the ones I hurt by lying to them or by getting into some kind of committed relationship with...only to cheat on them and get caught. These are the ones I regret and actually feel pretty bad about.
As far as getting shit tested by being accused of being a player; I usually say, with a grin and maybe a fake straightening of my jacket:
Well, I wouldn't go as far as to call myself a player but Daddy does okay; that's all I'm sayin'. 