How to see things to compliment?

Compliments are nice to receive (for most, not for me yet, but I'm working on that) and something one should be giving out. There's one thing – they should both be genuine and sound genuine. And as I am walking down a street, earning my foodmoney at work, shopping or in pretty much any "seeing people" situation, I just don't see anything worth complimenting. Like, I see a guy with a normal hairstyle, in a normal jacket, normal pants and normal shoes, and there's just nothing that comes to mind beyond "yeah, that's a normal guy". So genuinely complimenting people cannot happen. How to fix that? How to learn to notice nice things about people?