Here's a list of what you can add to your stories to make your sex scenes hotter:
The characters really shouldn't...and that's what makes it so sexy.
Maybe their boss is in the next room and might overhear or they're trying to join the mile high club.
If it's against the rules, it's hot. Making the reader feel that maybe they shouldn't be reading this story either because it's so taboo, but they read it anyway, will add to the excitement.
It's easy to write a scene where the two characters fall in love and then have sex. But the problem is, it's sweet, but not very hot. People want desire to be the driving force between the two characters.
To amp up the desire in the scene, you need to make the sex inconvenient. Because it's easy for two characters to have sex when the mood and setting are right, but it shows just how much two characters desire each other if the setting and mood are totally wrong, but they are still all over each other.
Like when two characters fight and that leads them to make love in the middle of the kitchen when they know at any minute one of their room mates might come home. It's hot because it shows that the two characters desire each other so much that they don't care if the counter tops are hard or if they are furious with each other or if someone might walk in. All they care about is having sex.
You don't have to go to an extreme to add some kink to your story. Maybe the characters don't use handcuffs, but the guy pins her to the bed with her hands over her head so that she can't move. Or he pulls out a vibrator because he wants to experiment on her.
Adding a little kink can go a long way to show just how much the characters desire one another.
Emotional turmoil will immediately make a sex scene hotter. She's not sure about a guy, in fact, she has every reason to hate him, but the way he pulls off his shirt and flexes his biceps as he does so is irresistable to her.
When a character feels tortured by her emotions, but still has sex anyway, it shows that lust is ruling her decisions. It makes the scene a little naughty because she's going against her mind to follow her desires because she feels so passionate that she just can't wait.
There is torture in BDSM, but that isn't necessarily the kind of torture I am talking about. (Although it can work, too.) I mean that two characters really want each other, but circumstances make it impossible for them to be with each other yet. Maybe they are in the middle of a crowd of people or they're driving somewhere or have immediate responsibilites that they need to attend to. They keep looking at each other with desire, maybe whispering about how they feel, but they have to wait and they can barely stand it.
After all that torture, when the characters finally get to have one another, the pay off is great.
On the other hand, you should avoid these crutches when trying to make sex scenes hotter....
1. Something New
A lot of people know what they like sexually and are just looking for a sexy story that satisfies those desires. They don't need something new to happen. They just need new characters and a new setting. The story will feel brand new, even if it isn't.
If you get too crazy about trying to add something new then that's when you have scenes that might scare your readers.
Like, imagine if a woman took a nutcracker and decided to use it on a man the way the name implies it should be used. I've never read a sex scene like that. It would be a very unique idea, but I would feel disturbed reading it.
2. New Positions
Some authors worry that if they always write sex scenes where the girl is on top or the two people are doing missionary that it will bore the readers after awhile. That's not true. It's the circumstances that surround the sex that makes the sex steamy.
Just do whatever fits the scene and makes the most sense. If the two characters are feeling adventurous, have them try out a new position. If they are having sex for the first time, though, they might stick to missionary. If they are having sex in a public restroom, missionary would be disgusting and likely lead to stickiness all over their bodies from rubbing up against the floor. In that situation only sex while standing up would make sense. If the main character is a strong woman, then maybe she likes to be on top, so she can take control.
Character personalities and setting will likely dictate which position is appropriate.