
Complement something you admire about them, like how they think or what they do. It might seem silly but women get so many looks compliments that it feels transactional or even just mundane to receive one. If you don’t know them enough to know those things then compliment a physical choice they’ve made (hairstyle, clothes, shoes, etc. or if you want to be really intimate about it, lean in and comment on their perfume). It will set you apart enough that they’ll actually take notice.
Even if the compliment isn’t about looks specifically depending on how you say it, it definitely will be heard that way anyway. But be careful because it can easily become sketchy and put you on the same level as any cat caller. I’d practice with a female friend if I were you. And remember: humility and the ability to laugh at yourself is much sexier than overconfidence.