"That feels so good, do that…" Or, "I love that you're pulling my hair, do it harder." When you whisper into someone's ear what they are already doing well, tell them you want more of "that" (whatever "that" is). It will make them want to keep going and turn them on.
When the heat between you is turned up, it's time to tell them something you'd like to try. You can say things like "I can't wait to feel you even closer to me," or "I'd love to lick your neck right now." Telling your partner what you are going to do can send them through the roof once they're already turned on. If your partner is a little reluctant to talk dirty, keep the talking at a gradual pace. Talking about sex during sex is something that some people find new, and they may feel awkward at first.
If you are just starting out, the secret is to whisper in your partner's ear. You don't have to make eye contact; just let them know "This is what I'm going to do to you…" Starting slow and measuring their reaction by how responsive they become will help you to judge their comfort level. You don't have to use "bad" words or swearing to get your point across. And don't worry if they seem surprised at first. Talking dirty is supposed to be a little shocking. That's the fun of it.
Dr. Tammy Nelson is a sex and relationship expert and the author of The New Monogamy as well as Getting the Sex You Want. She speaks internationally on global, relational change. She can be found at www.drtammynelson.com.