I advise them to say as little as possible. Some people just roll their window down about an inch, give the license, registration and proof of insurance and not say anything. This would really annoy the police, but if the person was able to do this, they would have a really good chance of beating the DUI.
Someone who was arrested for a DUI and did not agree to a chemical test (breath or blood) at the police station would still lose their license for an additional year whether or not they were convicted of a DUI. The best idea is to use a designated driver or just call Uber, instead of drinking and driving.
Even if the police officer was very nice and said the person was really cooperative, it usually doesn’t matter. If there was evidence the person was driving under the influence because they failed the field sobriety tests, the officer had probable cause to arrest them, no matter how cooperative they were. I often say, “What do a criminal defendant and a fish have in common? If they hadn’t opened their mouth they would not have been hooked.”