The problem is that every attempt to write such content ends up reading like it was written by a horny 13 year old...
Any suggestions?
The most important thing to remember is that good sex scenes require as much practice and skill as battle scenes, conflict scenes, introspective scenes, etc. So your first attempts are going to appear as out of practice as your first attempts at writing a mystery or a western.
One of the great books on this subject is 'The Joy of Writing Sex' by Elizabeth Benedict. Her principles have guided my smut writing every since. Also, let's not forget reading lots of such scenes to get a proper feel for them.
I've written perhaps 100 sex scenes, and here are a few tips. Your mileage may be different. They work for me.
1. First person seems more intimate than third.
2. I always write from the pov of only one of the participants. I don't head-hop between them. There are less confusing ways of showing what the non-pov participant(s) is/are thinking.
3. Make the emotional side more explicit and detailed than the physical side. There aren't that many ways to put Tab A in Slot B, but the range of emotions during a sexual encounter is unlimited.
4. Slide into the scene slowly, or even sideways. Boy and girl don't always meet, exchange the time of day, and start fucking in the same paragraph (unless they've been at it a lot).
5. Not all sexual encounters are successful. Some end in frustration, aborted orgasms, interruptions, etc.
6. Write about the kind of sex you like, not what the 'market' wants. I'm a confirmed heterosexual, and cannot write a gay sex scene to save my life. I don't have the experience. Neither do I like reading or writing stories where men dominate or abuse women.
7. If it doesn't give me a stiffy, I don't think it's going to give my reader one either. (This is really a corollary to #6.)
8. Make sure your reader knows early on just how explicit the book is going to be. In my WIP, it took me five chapters before the first piece of clothing came off. My publisher suggested adding a chapter at the beginning with an explicit scene that would flag it as a female-domination story. The lesson here is, don't fool your reader into thinking the novel is more or less explicit, or a different subgenre than it is.