If you've been in a relationship for a while, sex is probably down to a science.
Though you have it down stroke for stroke, you can make it better with a little dirty talk. And it doesn't have to be the porno variety all the time. I mean, throwing in a "fuck me harder and faster" is cool, but it's going to get redundant.
If you want to talk dirty, take a few hints from books, not movies.
Or just use your imagination and think back to the days when your relationship was fresh and new. Remember the things you did, things that were done to you? Talk about it in lush details, maybe even act out some of it.
Throwing in a explict word is cool, but no woman wants to be called a slut, unless you're role playing. Some women also balk at being called a bitch, so it might be wise to have a conversation about what she likes before hand. Or if you want to keep the heat of the moment, just avoid certain words all together. If it's good, there is sure to be a repeat performance and a chance to try out other words.