What convinces is conviction. Believe in the argument you're advancing. If you don't you're as good as dead. The other person will sense that something isn't there, and no chain of reasoning, no matter how logical or elegant or brilliant, will win your case for you.
“A good thing is I've been playing tennis I think every day for the last two months. I really haven't had a day off. I've been doing things that I did used to do.”
“This country would be a better place to live in if all the resources we currently put toward criminalizing marijuana were instead spent by law enforcement on protection from real crime, as opposed to victimless crime.”