Rule #1: Set Clear Expectations
You must discuss what you expect out of the sex you have with your friend. That includes telling him that you do not want to be his girlfriend, and you do not want to feel obligated to do anything for him. The sex will only be about the sex, and not about the friendship or it turning into a relationship.
Rule #2: Pay Attention to Emotions
Many women can't help but attach themselves emotionally to their sex buddy. While this is perfectly normal, it's a disaster in the making for the situation. It's important to keep your emotions in check when you have a friend with benefits. As soon as you feel yourself growing fonder of him, it's time to re-evaluate your friendship status.
While it may not seem likely now, many people start as friends with benefits, and then embark on a full-blown, committed relationship. So don't completely discount it as a possibility.{relatedarticles}
Rule #3: Avoid Jealousy
Your friend with benefits can be interested in someone else. He can go on dates, and he can have sex with other people.
The meaning behind, "no strings attached" means you hold no right to him. He is not yours, and he doesn't have to do anything before considering what you might think or feel about it.
This is one of the reasons why many people don't make it far with this type of arrangement. They can't cope with the person they are sleeping with having sex with someone else or going out on dates with other people.