In almost every role and walk of life there is a need to influence other people. From direct sales to advertising to interviews, influence is everywhere. Influence, though, is an art, and one that needs to be understood. What works in one situation may not work in another. In other words, the effectiveness of any influence technique can be situational. The good news is that considerable research has been conducted on influence. In his book, Influence: The Psychology of Persuasion, Dr. Robert Cialdini identifies six universal ways to influence others.

1. Reciprocity. This is based on the idea of "matching" what others have done for you. If you do a favor for someone, that person is more likely to help you if asked. Most people don't like to feel in debt to others, and will look to restore equilibrium. Booths in stores with sample food and giveaways at conventions are intended to make people more susceptible to buy after taking something. Interestingly, Adam Grant in his book Give and Take shares research showing that people that "give" judiciously do better in the long run than those that consistently "take."

2. Commitment (and Consistency). If you can get someone to verbally--or better yet, publically--commit to something, they are more likely to follow through with it. If you leave a meeting without agreeing to a course of action, less is likely to happen than if each person states their commitments out loud. Consistency is also important for two reasons. First, people that are consistent are more trustworthy, leading others to lend their support more readily. Second, people have an innate pull to remain alinged with what they have said or agreed to previously.

3. Social Proof. In game shows, if the audience is polled they are often quite accurate based on the pooled knowledge they have. People also look to others for validation. Watch kids sometime to see this in action. Once the damn breaks and one kid tries something, the others are likely to think it is okay and start doing the same thing. Testimonials and the use of "experts" and doctors (think, "9 out of 10 doctors recommend...") are all examples of using social proof to influence others.

4. Liking. There is perhaps nothing better for influence than being liked, which is related to being trusted. We also like people more who are similar to us and attractive people are typically found to be more likable. Likability is so important that it can often tip the scales in presidential elections. If someone likes you they will be more inclined to say yes to you.

5. Authority. This is one of the most dangerous types of influence. It can be the absolute most powerful, but it can also be the most corrupting if used to the extreme. Stanley Milgram showed the great lengths people will go to in order to obey authority. In some cases, participants in his experiment delivered what they thought was a crippling shock to another person, simply because they were told they had to do so by a person in the study that they thought was a real doctor. These titles, uniforms, and other visual displays of authority go a long way towards influencing people.

6. Scarcity. Think of all the commercials you have seen where you must "act now" or "time is running out" for a certain product. These commercials use scarcity to make people believe that a product has limited supply and that they must buy right away. If you can create urgency around something people will be more likely to act upon it or buy.