Once again, every situation is different, and yet there are commonalities.
My basic philosophy is this: Humans are animals, and despite the development of our wonder brains and all the rules and laws and civilizations we've built that we like to think put us above the lesser creatures, we're still slaves to our biology. When you're kissing her, the smell of her breath will be nice. This will trigger a pheremonal response in you; in other words, you'll get turned on. You will also emit pheremones which she, if she's ready, will also respond to. Things escalate from there. That's why in movies and on TV, the cliché is always physical proxmimity and contact, making out, then clothes start coming off. Unless you're both already horny as hell, you have to work up to it. This tends not to happen with couples who have not been intimate before.
The first couple of times you make out, you may enjoy it just fine but feel no twitching between your legs. Don't worry about it; let it happen naturally. Natural is always best; rushed and doing it because you think you should is not going to result in success. If you're compatible, at some point Mother Nature will take over and you'll start feeling more than just "fine" and start feeling more than just physical attraction. You'll harden up and feel the urge to stick it in her. Crude, yes, but that's exactly what is happening at that point; your animal instincts have taken over. The best thing you can do is guide them using your brain, which is slowly losing the battle for control of your actions, mostly because it's never had to contend with another part of your body for dominance before, and it isn't used to the competition.
If you're compatible, the same thing is happening to her. She too has chemicals rushing through her body, telling her to use it, to receive you. It's all biology. But she's having a similar struggle. Her brain is full of all the stuff she's accumulated over the years, telling her it's wrong, questioning whether you're the one, already thinking about tomorrow and if she'll feel guilty or fulfilled or a real woman or just a whore. Your goal is to overcome all this, but actions speak much louder than words. If you try to reassure her, you'll just sound like a guy feeding her lines to get her clothes off, because that's exactly what you are at that point. Instead, do it physically. Slow down. Hold her a lot, kiss her a lot but don't smother her and don't try to turn her on. Against everything you're feeling, it must happen on her schedule, not yours. She must be comfortable. If you do anything she's not ready for and willing to do, not only will the sex be bad, but you're a rapist and a bad guy, which is much worse. There will be other women, but not in prison.