Involve the reader by describing physical feelings and emotions, as well as actions. Aim to get some rhythmic flow into your writing that carries the reader on smoothly from one piece of the action to next. Remember we have five senses and write to appeal to all of them. Dialogue can be useful, but more in the build-up to the sex scene than in the scene itself, where it should be used sparingly. Make use of your knowledge of the different ways people make love and imagine new ones, new settings, to get as much variety as possible into your writing.
All writers are also readers.
Your job as a writer is to put yourself in the position of a reader coming to your book for the first time. It's not easy, but once you've mastered the trick it will pay dividends. Then you'll know how to edit your writing. Read 'How To' books if you must, but develop your own way of working. Every writer works differently.