Sex is "promiscuous" if it lacks the following safeguards:
1. Compiling of evidence WRT STIs. That is, I know how clean I am and how clean you are. Maybe I trust you to tell me the truth, or maybe I want to see actual documentation. But I have proof and you have proof. Yes, "we're both virgins" is evidence...but only if it's true.
2. Discussion (and genuine agreement) of what to do in the event of STIs/pregnancy. Now, not everyone has heterosexual vaginal intercourse, but if you're planning on it, you really should consider the possibility of whether the species will try to propagate itself through you. Similarly, not everyone has a STI, but tests are sometimes inaccurate...and sometimes people do have STIs and still want sex with you.
3. Discussion of preferred techniques and hypothetical goal scenarios. Honestly, if you're going to be having sex at all...you might as well give your partner a pretty good idea of what you're hoping to achieve.
4. A night to sleep on it. This is probably the item that's going to generate the most discussion. Is it really necessary to sleep on it? I think the answer is yes. I think it's important when you start a sexual relationship to be able to walk away before fluids get transferred (As the Laws of Thermodynamics tell us, it's really hard to untransfer fluids). And the only real polite way to give your partner (or yourself) that out is to go your separate ways long enough for sexual excitation to completely settle down, for the mind to truly cycle and ruminate on the subject. In short, to sleep on it.
Done all those things? Great. Fuck like things that fuck a lot (or those that only fuck a little), as is your wont.