Many couples enjoy bondage or S&M types of sexual play, although this is a broad category that can really run the gamut from mild to wild. For some, it may simply mean using a paddle for some light spanking or furry handcuffs for harmless restraints. Other couples are into more hardcore types of activities: leashes or collars and serious restraints, hot wax, whips, etc. The important thing is to make sure you and your partner are both comfortable with the choice of S&M tactics.
When engaging in S&M activities, many couples find it important to have a safe word, which would signal that they want to stop immediately. This word should be something obscure, as opposed to a common word like “No!” which people often blurt out instinctively in the heat of passion. Both partners must respect this rule and agree to abide by the signal word.
It is not uncommon for people to be more turned on by the idea of being tied up, punished, or whipped than they are by the actual reality. Often, one or both partners will realize these S&M tactics may be more painful and/or embarrassing than they had expected. So it's a good idea to start on the mild end of the spectrum — say, by tying each other up with scarves or engaging in light spanking — and slowly working your way up to more daring stuff if you feel comfortable.
If you are really serious about pursuing your S&M fantasies, you may even want to try to find a dominatrix in your area. These are women who specialize in performing dominating — and sometimes abusive — techniques in order to stimulate sexual arousal in their clients. (They generally don't actually have sex with clients, though.) Some even provide instructional services, where they will teach one person how to better employ domination techniques with a submissive partner.