It's no good ranting and yelling if you want to win an argument. What you need is a strategy.
1. Listen to what the other person is saying and let them share their views in full before making your case. This means they are more likely to listen to you and you can alter what you say to address their specific concerns
2. Make the other person feel good about themselves. If you can give compliments without seeming too obvious (or obsequious), then do so.
3. Find out why the other person has a different view to you. You may be able to meet their real needs (eg, wanting you to consider them an equal) in another way, which will allow them to be convinced by your argument more easily
4. Ask questions. People are much more likely to change their mind if they have talked through your argument themselves rather than listening to you make it.
5. If you are presenting a rational argument, be sure that your facts are correct. If one element of your case is shown to be false, it will reduce the credibility of everything else you say.
6. If possible, link your position with the other person's values or aspirations. Emotional reasons can be just as powerful as rational ones.
7. Showing that others agree with you can help support your case but is rarely sufficient to win the argument – when was the last time you chose a supplier entirely because of their client list?
8. Differentiate between the substance of the disagreement and the two of you as people. Focus on what they are saying (they believe advertising has no effect) rather than what you think about them as a result of their position (they are stupid)
9. Make your argument simple and with a clear structure. If you write down the main points first you are less likely to jumble them up and so more likely to convince.
10. Remember that people make decisions for their reasons, not yours. Adapt your argument to the person you are trying to win over, every time.