Editing is editing when it comes right down to it. There are things you'll always look for: grammar, spelling, wordiness, readability. But editing erotica has it's own special things you need to watch for, whether you're editing your own or other's work.
There are only so many times that readers can stand reading those euphemisms for body parts. If you use the c*ck word or the pu**y word over and over again in a story, your readers will get bored! Mix it up! But keep in mind that certain words do not go with certain types of stories. If you are writing erotica that leans more towards the romantic, you don't want to use the hardcore words that are going to scare your readers away. If you're writing hardcore erotica that leans more towards porn, heaving bosoms just are going to do the trick. Choose your words carefully and try to add some variety.
The dragging scene
Yes, there is such a thing as too much sex. In good erotica anyway. If you're writing jerk off material, you can put as much sex as you want in there, but even then, you're readers will drift away or skim down to the good parts if your scene drags on too long. If you're writing erotica for a discerning type of reader, they want to know why she likes being spanked, how she feels about the man with his tongue in her ... Get the picture. Erotica is not just about sex. It's about the people who are having sex and everything that is going on in their minds. Don't be afraid to reveal some of that.
Cliches are never good in any writing but especially in erotica they should be strictly avoided. If you can find half a dozen other stories that use the exact same phrases as you've used, then it is cliche. Try to think of some new and original phrases and comparisons. But make them match your subject. Sorry guys, but most women don't want to be compared to a car!
Edit your erotica thoroughly for grammar, spelling, wordiness and readability - please - but keep these things in mind as well!