Not sure it's the best I ever received, but it's the one that comes to mind. From my dad: "When asking someone out, don't ask 'what are you doing this weekend?' It's none of your business what they're doing. Ask 'can I take you to dinner this weekend?'"

She was looking for an excuse to say no. Thanks to my dad's advice, I didn't give her one. So she let me take her out. That led to the next 30 years...

Thanks, dad.

(For those who are really soured on marriage: No, that wasn't sarcasm. I am genuinely thankful for the advice, and for where it led me.)