Supply and demand is simple: supply the product as much as possible without falling below or exceeding demand. In order to enter or continue any relationship without getting canned, "selling" yourself becomes important. Even more importantly, avoiding supplying too much or too little of yourself is important. The wrong amount of supply can result in decreased profit (e.g. emotional support, social benefit and sexual pleasure). Here are some tips: Phone etiquette -- People who are "high suppliers" are dodgy types that try to spend so much time with you that it seems like they enjoy watching you brush your teeth. These people tend to break my personal golden rule of phone etiquette. The rule is that if you leave a voice mail message, under no circumstances should you call again within 48 hours, unless you get a return call. Here is another tip: If a couple lives in the same town and either one wants to talk on the phone for more than 10 minutes a day, I would bet dollars to doughnuts that the other person hates it. Even though that guy who you dated three relationships ago loved it when you told him about your favorite "Sex and the City" reruns, chances are you will be playing alone this weekend if you don't stop talking. Low suppliers many times will not return calls until days later, if at all. If you aren't returning phone calls within 24 hours, you'll probably be catching Friday night reruns too. Another good way to gauge if you are spending too much or too little time around your flavor-of-the-week is facial cues. Here are some popular ones that, if you see, you need to back off a touch: lack of eye contact, playing with hair or hands, being easily distracted, refusing to continue or start conversations and smiling at others during conversations but not smiling at you. Personally, I believe the most telling body cue is the position of the shoulders. If someone is interested in what you are saying, their shoulders will both be facing you and the person will lean towards you slightly. Those who are uninterested usually will have one shoulder pointed at you and the other pointed away from you, most likely toward a large open space in the room. When you see this, you will know for a fact that there is something more interesting than you in that room. Obviously, whether you are a high supplier or a low supplier, the correction to make is obvious: take a step back or a step foreword. Picking up on subtle hints that show you how much space you need to give will make or break any relationship. And by the way, make sure you wrap it up kids. Next Time: How to spot a bargain. Colin Clark is a Cavalier Daily Health & Sexuality columnist. He can be reached at email@example.com.