Good negitiating skills?

I am trying to settle some cc debts that are still around 60 days from chargeoff.

I keep seeing that you need good negotiating skills, any tips on what not to do or say as well as any tips that would help?

For example, amex, later this month I will be at 120 days since my last payment, offered them approx 28%, they only say can you come up with more money, they are at 85%.

Thanks