Read and Write

My best advice for new writers looking to hone their craft is: Read and Write.

Read

Read books. Read good books. Read bad books. Read lots of books.

Good books can give you ideas, present writing concepts you had never thought of, and teach you new interesting words, etc.

Bad books can show you how to write an unlikable uninteresting protagonist that drags down the story, how to meander in your storyline until you lose the reader's attention, what tropes don't mesh well with others, etc. Learn from mistakes made by other people.

Write

Writing is an art and a craft. And, like other arts&crafts, you get better at it by doing it repeatedly.

You want to get better at writing erotica? Write some, even if you don't think it's any good. You can publish it if you want, but you don't have to. You're allowed to write things just for yourself, just to practice, just for fun.

Then, reread your writing. Especially after a while, once you've detached yourself from the writing process with a few days or weeks. You'll see the mistakes you make, the things that can potentially drag down your texts. Is there a word, expression, or sentence that you repeat way too often? Change it up, find different ways to say it, look for synonyms in a thesaurus. Are your characters compelling? Why? Or why not?

One great way that beginner smut writers can practice their craft is through ERP (Erotic Role Play).