Let them speak first. Listen, identify their concerns (getting promoted, closing a deal) and then tailor an irresistible argument.
Give them credit. Ask questions that guide them to your conclusion. Who'd reject an idea they've come up with themselves?
Stay calm. Focus on what your opponents are saying rather than what you think of them as a result of it (they're a fool). Calm a rising temperature by asking yourself what you want to achieve and how you can make it happen.
Be prepared. Write down every challenge your argument could provoke, hone your answers, then practise delivering them.
Don't bamboozle. Most people would rather reject an idea than admit confusion. Break your argument into bite-size chunks, simplify and clarify. Make it foolproof.
Strike a match. Feeling a connection with others makes us more open to their ideas. Give natural synergy a nudge with body language. Adopt their posture, laugh when they laugh.
Reason with them. Of the nine major influencing tactics, logical reasoning is the most effective: saying 'because' after a statement increases the percentage of those converted by 50%. Reinforce your argument with accurate facts and figures.
Get emotional. Logic not working? Go for the heartstrings. Align your argument with your opponent's values and aspirations and paint a glowing picture of the future you want.
Flatter. 'I know that you of all people will be able to cope with the new process I'm suggesting.' Just don't overdo it.
Use your allies. Refer to someone they respect. The more it appears you're widely supported, the harder it will be to reject.
Believe. If you're not convinced, why should they be?