When you can, back up what you say with real facts. Lying will only convince somebody until they find out about the lie, then you will never be able to convince them of anything again.
Be willing to be convinced. Sometimes accepting one point from the other person and showing that you can change your mind when you are wrong will help them to be the same, and change their mind about the subject you care about.
Practice active listening. Active listening helps you control a conversation and keeps it on track. Active listening techniques include:
Non-verbal feedback. Nodding your head as the other talks etc.
Paraphrase what the other person has said to make sure you understand it.
Make sure you understand the other person's objections and respond to them in an intelligent manner.
Keep vigilant about your belief, but always respectful of the beliefs of others. Explain why your belief is important to you.
Understand the other person's motivations. If you know what another person wants, you are more likely to be able to give it to them.
Rephrase your beliefs in a way that the other person is better able to understand.
Follow up. Ask questions to make sure the other person understands their new views completely.
Tips
To hold the eye of a crowd select individuals in the crowd and hold their eyes on-and-off through your presentation.
Never lose your cool. Nothing lacks conviction more than a raving idiot.
Always be friendly and respectful even if the other person does not change their mind.
Beliefs fade. You may think you have changed somebodies mind but find that in a day or two, perhaps a week, they are right back to where they were before.
Buy and read some books on sales techniques.
Concluded
