All I can do here is give you some ideas about what's worked for me and perhaps some ideas about the pitfalls of steamy scenes.
He put what where?
Steamy scenes shouldn't just relate who did what to whom. If that's all you do, your scene is going to feel clinical and not at all sensual. As with any scene, steamy or not, you need some foreplay. (Ha!) That means your previous scenes should build the tension between your hero and heroine so that when your heroine does permit this incredible intimacy, it's believable that she should do so.
Feelings and Consequences
Steamy scenes are as much about emotion as they are about sex. I've read extremely "steamy" scenes where there's very little description about what they're actually doing. They succeed because sex scenes are about emotion. If you write about your hero touching the heroine in some intimate manner, try to include the emotion of his so doing. Don't just say that he felt incredible pleasure. The same goes for the heroine, and don't forget to keep in mind that the stakes are higher for her.
It's easy to feel as though once your h/h have sex, it's all downhill from there. But it's not. A sexual encounter can actually make the hero or heroine more insecure.
Things to Keep in Mind
Contraception was not reliable. Getting pregnant is a real consequence of sex, and I don't feel this should be ignored. If your heroine is so naive as to not know how babies get made (hmmm) then your hero needs to be thinking about it. Or, of course, you need to have put them into a situation in which the failure of think about it is believable without making your hero a jerk and/or your heroine an idiot.
Some Frank Talk
Heroines are often virgins. But not always. I've noticed that most virginity scenes involve language and reactions that are becoming a bit trite. If you've been reading in the genre, then you know what I mean. He warns about pain, she cries and gets over it right away. Or he knows she's a virgin and doesn't warn at all, which to me makes him stupid and unfeeling. Be aware of this and write carefully. What keeps your scene from being trite is emotion and set-up.
Heroines hardly ever, uhm, do this for the hero or if they do, he stops her before he climaxes. Heroines are almost always on the receiving end, and I think most women readers of this page know exactly why. I pity all those poor heros who don't get equal pleasure. Your choice, your scene, but there are two people and their anatomy is different. Vive la difference!
Clothing, or the Lack Thereof
I'm getting tired of the number of heros who are able to easily expose female body parts that, in reality, were firmly covered by corsets, chemises and bodices. Sorry, but you need to take clothing into account.
Oh, well. Once you get going, it's fine. But if you're worried what your friends, family and co-workers are going to think about you, be prepared for mediocre sex.