Well-written erotica needs to be a full-body experience, immersing the reader in all five senses.
While the first time I read erotica, I was turned on just by seeing explicit language on the page, that quickly grows old unless it's freshly described. After reading a whole bunch of erotica, I was left with almost no desire to read about "the old in-out" unless the writing is revealing some new aspect.
Nothing can beat a truly fresh description, a brilliant metaphor unique to an individual writer, but broader lists of words can also help.
I use the thesaurus more now than I ever did before. You can also find specialized lists, such as this erotic thesaurus.
The great challenge of erotica is to write over and over again about the same type of action and make it feel new and thrilling every time. Plenty of elements go into that, but a big part of it is fresh, sensual description.
The other day, I was writing a story that included a section where I really wanted to focus on smell and taste. Those senses are very central to my experience, but maddeningly difficult to describe. I was looking for a fresh set of words, and found this useful post, which helped me to consider types of smells and tastes apart from my usual go-tos. (Bonus note: It amuses me that the comments to the post I linked seem split between schoolchildren and erotica writers.)