Had a long conversation on a train with a woman who, for some reason, told me, "Do you want to flatter a woman? Complement her shoes. Women put a lot of time into shoes, and if you let her know you noticed, it simultaneously compliments her beauty, intelligence, and fashion sense, without looking like a dopey pick up line, completely validating her for at least a few minutes. Don't be too specific or do it too often as then it gets creepy."
Probably one of the best pieces of advice I have ever received, and I can't even tell you the woman's name.